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Please refer to the License Notice in the Appendix. In , it culminated in a language reference manual, in Russian. At the instigation of Alexey Kovyazin, a campaign was launched amongst Firebird users world-wide to raise funds to pay for a professional translation into English, from which translations into other languages would proceed under the auspices of the Firebird Documentation Project. This Firebird SQL Language Reference is the first comprehensive manual to cover all aspects of the query language used by developers to communicate, through their applications, with the Firebird relational database management system. It has a long history. Firebird conforms closely with international standards for SQL, from data type support, data storage structures, referential integrity mechanisms, to data manipulation capabilities and access privileges. These are the areas addressed in this volume. The material for assembling this Language Reference has been accumulating in the tribal lore of the open source community of Firebird core developers and user-developers for 15 years. However, it came without rights to existing documentation. Once the code base had been forked by its owners for private, commercial development, it became clear that the open source, non-commercial Firebird community would never be granted right of use. The former covered the data definition language DDL subset of the SQL language, while the latter covered most of the rest. Fortunately for Firebird users over the years, both have been easy to find on-line as PDF books. From around , Paul, with Firebird Project lead Dmitry Yemanov and a documenter colleague Thomas Woinke, set about the task of designing and assembling a complete SQL language reference for Firebird. They began with the material from the LangRef Updates, which is voluminous. It was going to be a big job but, for all concerned, a spare-time one. By the end of , they had the task almost complete, in the form of a Microsoft Word document. The Russian sponsors, recognising that their efforts needed to be shared with the world-wide Firebird community, asked some Project members to initiate a crowd-funding campaign to have the Russian text professionally translated into English. From there, the source text would be available for translation into other languages for addition to the library. The fund-raising campaign happened at the end of and was successful. In June, , professional translator Dmitry Borodin began translating the Russian text. Certainly, we never have enough translators so please, you Firebirders who have English as a second language, do consider translating some sections into your first language. The first full language reference manual for Firebird would not have eventuated without the funding that finally brought it to fruition. We acknowledge these contributions with gratitude and thank you all for stepping up. IBSurgeon ibase. Distinct subsets of SQL apply to different sectors of activity. Procedural SQL augments Dynamic SQL to allow compound statements containing local variables, assignments, conditions, loops and other procedural constructs. Interactive ISQL refers to the language that can be executed using Firebird isql , the command-line application for accessing databases interactively. As a regular client application, its native language is DSQL. It also offers a few additional commands that are not available outside its specific environment. SQL dialect is a term that defines the specific features of the SQL language that are available when accessing a database. SQL dialects can be defined at the database level and specified at the connection level. Three dialects are available:. Dialect 1 is intended solely to allow backward comptibility with legacy databases from very old InterBase versions, v. Dialect 1 databases retain certain language features that differ from Dialect 3, the default for Firebird databases. Date and time information are stored in a DATE data type. Double quotes may be used as an alternative to apostrophes for delimiting string data. Double-quoting strings is therefore to be avoided strenuously. Dialect 2 is available only on the Firebird client connection and cannot be set in the database. It is intended to assist debugging of possible problems with legacy data when migrating a database from dialect 1 to 3. Double quotes are reserved for delimiting non-regular identifiers, enabling object names that are case-sensitive or that do not meet the requirements for regular identifiers in other ways. Use of Dialect 3 is strongly recommended for newly developed databases and applications. Both database and connection dialects should match, except under migration conditions with Dialect 2. Processing of every SQL statement either completes successfully or fails due to a specific error condition. The primary construct in SQL is the statement. A statement defines what the database management system should do with a particular data or metadata object. A clause defines a certain type of directive in a statement. Options, being the simplest constructs, are specified in association with specific keywords to provide qualification for clause elements. Where alternative options are available, it is usual for one of them to be the default, used if nothing is specified for that option. All words that are included in the SQL lexicon are keywords. Some keywords are reserved , meaning their usage as identifiers for database objects, parameter names or variables is prohibited in some or all contexts. Non-reserved keywords can be used as identifiers, although it is not recommended. From time to time, non-reserved keywords may become reserved when some new language feature is introduced. For instance, the following statement will be executed without errors because, although ABS is a keyword, it is not a reserved word. On the contrary, the following statement will return an error because ADD is both a keyword and a reserved word. Refer to the list of reserved words and keywords in the chapter Reserved Words and Keywords. All database objects have names, often called identifiers. Two types of names are valid as identifiers: regular names, similar to variable names in regular programming languages, and delimited names that are specific to SQL. To be valid, each type of identifier must conform to a set of rules, as follows:. No other characters, including spaces, are valid. The name is case-insensitive, meaning it can be declared and used in either upper or lower case. It may contain characters from any Latin character set, including accented characters, spaces and special characters. Delimited identifiers are available in Dialect 3 only. For more details on dialects, see SQL Dialects. The reason is that Firebird stores all regular names in upper case, regardless of how they were defined or declared. Delimited identifiers are always stored according to the exact case of their definition or declaration. Thus, "FullName" quoted is different from FullName unquoted, i. Literals are used to represent data in a direct format. Examples of standard types of literals are:. Details about handling the literals for each data type are discussed in the next chapter, Data Types and Subtypes. Some of these characters, alone or in combinations, may be used as operators arithmetical, string, logical , as SQL command separators, to quote identifiers and to mark the limits of string literals or comments. A comment can be any text specified by the code writer, usually used to document how particular parts of the code work. The parser ignores the text of comments. Text in block comments may be of any length and can occupy multiple lines. In-line comments start with a pair of hyphen characters, -- and continue up to the end of the current line. A data type of a dynamically variable size for storing large amounts of data, such as images, text, digital sounds. The basic structural unit is a segment. The blob subtype defines its content. Size in bytes depends on the encoding, the number of bytes in a character. A fixed-length character data type. When its data is displayed, trailing spaces are added to the string up to the specified length. Trailing spaces are not stored in the database but are restored to match the defined length when the column is displayed on the client side. Network traffic is reduced by not sending spaces over the LAN. If the number of characters is not specified, 1 is used by default. A number with a decimal point that has scale digits after the point. Time of day. It cannot be used to store an interval of time. Variable length string type. The total size of characters in bytes cannot be larger than 32KB-3 , taking into account their encoding. The two trailing bytes store the declared length. There is no default size: the n argument is mandatory. Leading and trailing spaces are stored and they are not trimmed, except for those trailing characters that are past the declared length. Bear in mind that a time series consisting of dates in past centuries is processed without taking into account the actual historical facts, as though the Gregorian calendar were applicable throughout the entire series. Firebird does not support an unsigned integer data type. The shorthand name of the data type is INT. Numbers of the BIGINT type are within the range from -2 63 to 2 63 - 1, or from -9,,,,,, to 9,,,,,, Starting from Firebird 2. The usage and numerical value ranges of hexadecimal notation are described in more detail in the discussion of number constants in the chapter entitled Common Language Elements. However, this happens after the numerical value is determined, so 0x 8 digits and 0x 9 digits will be saved as different BIGINT values. Floating point data types are stored in an IEEE binary format that comprises sign, exponent and mantissa. Considering the peculiarities of storing floating-point numbers in a database, these data types are not recommended for storing monetary data. For the same reasons, columns with floating-point data are not recommended for use as keys or to have uniqueness constraints applied to them. For testing data in columns with floating-point data types, expressions should check using a range, for instance, BETWEEN , rather than searching for exact matches. When using these data types in expressions, extreme care is advised regarding the rounding of evaluation results. To ensure the safety of storage, rely on 6 digits. Fixed-point data types ensure the predictability of multiplication and division operations, making them the choice for storing monetary values. According to the standard, both types limit the stored number to the declared scale the number of digits after the decimal point. For instance, NUMERIC 4, 2 defines a number consisting altogether of four digits, including two digits after the decimal point; that is, it can have up to two digits before the point and no more than two digits after the point. If the number 3. Understanding the mechanism for storing and retrieving fixed-point data should help to visualise why: for storage, the number is multiplied by 10 s 10 to the power of s , converting it to an integer; when read, the integer is converted back. The method of storing fixed-point data in the DBMS depends on several factors: declared precision, database dialect, declaration type. Some more examples are:. Always keep in mind that the storage format depends on the precision. However, the actual range of values for the column will be If fractions of seconds are stored in date and time data types, Firebird stores them to ten-thousandths of a second. If a lower granularity is preferred, the fraction can be specified explicitly as thousandths, hundredths or tenths of a second in Dialect 3 databases of ODS 11 or higher. The actual precision of values stored in or read from time stamp functions and variables is:. Deci-milliseconds can be specified but they are rounded to the nearest integer before any operation is performed. Deci-milliseconds precision is rare and is not currently stored in columns or variables. The available range for storing data is from January 01, 1 to December 31, If, for some reason, it is important to you to store a Dialect 1 timestamp literal with an explicit zero time-part, the engine will accept a literal like ' However, '' would have precisely the same effect, with fewer keystrokes! It stores the time of day within the range from The method of storing date and time values makes it possible to involve them as operands in some arithmetic operations. An example is to subtract an earlier date, time or timestamp from a later one, resulting in an interval of time, in days and fractions of days. DATE increased by n whole days. Broken values are rounded not floored to the nearest integer. TIME increased by n seconds. The fractional part is taken into account. DATE reduced by n whole days. TIME reduced by n seconds. The collation sequence does not affect this maximum, although it may affect the maximum size of any index that involves the column. If no character set is explicitly specified when defining a character object, the default character set specified when the database was created will be used. If the database does not have a default character set defined, the field gets the character set NONE. UTF8 comes with collations for many languages. Non-accented Latin letters occupy 1 byte, Cyrillic letters from the WIN encoding occupy 2 bytes in UTF8 , characters from other encodings may occupy up to 4 bytes. The UTF8 character set implemented in Firebird supports the latest version of the Unicode standard, thus recommending its use for international databases. While working with strings, it is essential to keep the character set of the client connection in mind. If there is a mismatch between the character sets of the stored data and that of the client connection, the output results for string columns are automatically re-encoded, both when data are sent from the client to the server and when they are sent back from the server to the client. It can be characterized such that each byte is a part of a string, but the string is stored in the system without any clues about what constitutes any character: character encoding, collation, case, etc. It is the responsibility of the client application to deal with the data and provide the means to interpret the string of bytes in some way that is meaningful to the application and the human user. The database engine has no concept of what it is meant to do with a string of bits in OCTETS , other than just store it and retrieve it. Again, the client side is responsible for validating the data, presenting them in formats that are meaningful to the application and its users and handling any exceptions arising from decoding and encoding them. Usually, it provides nothing more than ordering based on the numeric code of the characters and a basic mapping of upper- and lower-case characters. If some behaviour is needed for strings that is not provided by the default collation sequence and a suitable alternative collation is supported for that character set, a COLLATE collation clause can be specified in the column definition. For a case-insensitive search, the UPPER function could be used to convert both the search argument and the searched strings to upper-case before attempting a match:. For strings in a character set that has a case-insensitive collation available, you can simply apply the collation, to compare the search argument and the searched strings directly. The following table shows the possible collation sequences for the UTF8 character set. Collation works according to the position of the character in the table binary. Added in Firebird 2. Case-insensitive collation, works without taking character case into account. Case-insensitive, accent-insensitive collation, works alphabetically without taking character case or accents into account. In Firebird earlier than version 2. Multi-byte character sets and compound indexes limit the size even further. The maximum length of an indexed string is 9 bytes less than that quarter-page limit. The table below shows the maximum length of an indexed string in characters , according to page size and character set, calculated using this formula. CHAR is a fixed-length data type. If the entered number of characters is less than the declared length, trailing spaces will be added to the field. Generally, the pad character does not have to be a space: it depends on the character set. A valid length is from 1 to the maximum number of characters that can be accommodated within 32, bytes. The stored structure is equal to the actual size of the data plus 2 bytes where the length of the data is recorded. All characters that are sent from the client application to the database are considered meaningful, including the leading and trailing spaces. However, trailing spaces are not stored: they will be restored upon retrieval, up to the recorded length of the string. In all other respects it is the same as CHAR. BLOB s Binary Large Objects are complex structures used to store text and binary data of an undefined length, often very large. Nowadays, it is effectively irrelevant. The segment size for BLOB data is determined by the client side and is usually larger than the data page size, in any case. Firebird provides two pre-defined subtypes for storing user data:. This is the subtype to specify when the data are any form of binary file or stream: images, audio, word-processor files, PDFs and so on. Subtype 1 has an alias, TEXT , which can be used in declarations and definitions. It is a specialized subtype used to store plain text data that is too large to fit into a string type. From Firebird 2. It is also possible to add custom data subtypes, for which the range of enumeration from -1 to , is reserved. Custom subtypes enumerated with positive numbers are not allowed, as the Firebird engine uses the numbers from 2-upward for some internal subtypes in metadata. The internal structures related to BLOB s maintain their own 4-byte counters. The following operators are supported completely:. Aside from that, there are some quirks:. By default, a regular record is created for each BLOB and it is stored on a data page that is allocated for it. The number of this special record is stored in the table record and occupies 8 bytes. If a BLOB does not fit onto one data page, its contents are put onto separate pages allocated exclusively to it blob pages , while the numbers of these pages are stored into the BLOB record. This is a level 1 BLOB. If the array of page numbers containing the BLOB data does not fit onto a data page, the array is put on separate blob pages, while the numbers of these pages are put into the BLOB record. This is a level 2 BLOB. Supporting arrays in the DBMS could make it easier to solve some data-processing tasks involving large sets of similar data. This example will create a table with a field of the array type consisting of four integers. The subscripts of this array are from 1 to 4. To specify explicit upper and lower bounds of the subscript values, use the following syntax:. A new dimension is added using a comma in the syntax. In this example we create a table with a two-dimensional array, with the lower bound of subscripts in both dimensions starting from zero:. The DBMS does not offer much in the way of language or tools for working with the contents of arrays. The database employee. If the features described are enough for your tasks, you might consider using arrays in your projects. Currently, no improvements are planned to enhance support for arrays in Firebird. It is not available as a data type for declaring table fields, PSQL variables or parameter descriptions. An evaluation problem occurs when optional filters are used to write queries of the following type:. This is a case where the developer writes an SQL query and considers :param1 as though it were a variable that he can refer to twice. The following example demonstrates its use in practice. Each named parameter corresponds with two positional parameters in the query. The application passes the parameterized query to the server in the usual positional? Firebird has no knowledge of their special relation with the first and third parameters: that responsibility lies entirely on the application side. Once the values for size and colour have been set or left unset by the user and the query is about to be executed, each pair of XSQLVAR s must be filled as follows:. In other words: The value compare parameter is always set as usual. When composing an expression or specifying an operation, the aim should be to use compatible data types for the operands. When a need arises to use a mixture of data types, it should prompt you to look for a way to convert incompatible operands before subjecting them to the operation. The ability to convert data may well be an issue if you are working with Dialect 1 data. When you cast to a domain, any constraints declared for it are taken into account, i. If the value does not pass the check, the cast will fail. When operands are cast to the type of a column, the specified column may be from a table or a view. Only the type of the column itself is used. For character types, the cast includes the character set, but not the collation. The constraints and default values of the source column are not applied. Keep in mind that partial information loss is possible. It may contain 1 or 2 digits or You can also specify the three-letter shorthand name or the full name of a month in English. A separator, any of permitted characters. Leading and trailing spaces are ignored. These shorthand expressions are evaluated directly during parsing, as though the statement were already prepared for execution. Thus, even if the query is run several times, the value of, for instance, timestamp 'now' remains the same no matter how much time passes. If you need the time to be evaluated at each execution, use the full CAST syntax. An example of using such an expression in a trigger:. In Dialect 1, in many expressions, one type is implicitly cast to another without the need to use the CAST function. For instance, the following statement in Dialect 1 is valid:. In Dialect 1, mixing integer data and numeric strings is usually possible because the parser will try to cast the string implicitly. For example,. In Dialect 3, an expression like this will raise an error, so you will need to write it as a CAST expression:. When multiple data elements are being concatenated, all non-string data will undergo implicit conversion to string, if possible. Creating a domain does not truly create a new data type, of course. If several tables need columns defined with identical or nearly identical attributes, a domain makes sense. Domain usage is not limited to column definitions for tables and views. Domains can be used to declare input and output parameters and variables in PSQL code. A domain definition contains required and optional attributes. The data type is a required attribute. Optional attributes include:. While defining a column using a domain, it is possible to override some of the attributes inherited from the domain. Table 3. Often it is better to leave domain nullable in its definition and decide whether to make it NOT NULL when using the domain to define columns. With this statement you can:. If you change domains in haste, without carefully checking them, your code may stop working! When you convert data types in a domain, you must not perform any conversions that may result in data loss. SQL expressions provide formal methods for evaluating, transforming and comparing values. SQL expressions may include table columns, variables, constants, literals, various statements and predicates and also other expressions. The complete list of possible tokens in expressions follows. Identifier of a column from a specified table used in evaluations or as a search condition. An expression may contain a reference to an array member i. Predicates used to check the existence of values in a set. The IN predicate can be used both with sets of comma-separated constants and with subqueries that return a single column. An expression, similar to a string literal enclosed in apostrophes, that can be interpreted as a date, time or timestamp value. A member of in an ordered group of one or more unnamed parameters passed to a stored procedure or prepared query. A SELECT statement enclosed in parentheses that returns a single scalar value or, when used in existential predicates, a set of values. Operations inside the parentheses are performed before operations outside them. When nested parentheses are used, the most deeply nested expressions are evaluated first and then the evaluations move outward through the levels of nesting. Expression for obtaining the next value of a specified generator sequence. A constant is a value that is supplied directly in an SQL statement, not derived from an expression, a parameter, a column reference nor a variable. It can be a string or a number. The maximum length of a string is 32, bytes; the maximum character count will be determined by the number of bytes used to encode each character. SQL reserves a different purpose for them. The character set of a string constant is assumed to be the same as the character set of its destined storage. Each pair of hex digits defines one byte in the string. Strings entered this way will have character set OCTETS by default, but the introducer syntax can be used to force a string to be interpreted as another character set. The client interface determines how binary strings are displayed to the user. The isql utility, for example, uses upper case letters A-F, while FlameRobin uses lower case letters. Other client programs may use other conventions, such as displaying spaces between the byte pairs: '4E 65 72 76 65 6E'. The hexadecimal notation allows any byte value including 00 to be inserted at any position in the string. However, if you want to coerce it to anything other than OCTETS, it is your responsibility to supply the bytes in a sequence that is valid for the target character set. This is known as introducer syntax. Its purpose is to inform the engine about how to interpret and store the incoming string. In SQL, for numbers in the standard decimal notation, the decimal point is always represented by period. Inclusion of commas, blanks, etc. Exponential notation is supported. For example, 0. Hexadecimal notation is supported by Firebird 2. Hex numbers in the range That changes the type but not the value. Since the leftmost bit sign bit is set, it maps to the negative range The sign bit is not set now, so they map to the positive range This is something to be aware of. Hex numbers between SQL operators comprise operators for comparing, calculating, evaluating and concatenating values. SQL Operators are divided into four types. Each operator type has a precedence , a ranking that determines the order in which operators and the values obtained with their help are evaluated in an expression. The higher the precedence of the operator type is, the earlier it will be evaluated. Each operator has its own precedence within its type, that determines the order in which they are evaluated in an expression. Operators with the same precedence are evaluated from left to right. To force a different evaluation order, operations can be grouped by means of parentheses. Arithmetic operations are performed after strings are concatenated, but before comparison and logical operations. Comparison operations take place after string concatenation and arithmetic operations, but before logical operations. Character strings can be constants or values obtained from columns or other expressions. Combines two or more predicates, each of which must be true for the entire predicate to be true. Combines two or more predicates, of which at least one predicate must be true for the entire predicate to be true. A step value of 0 returns the current sequence value. A conditional expression is one that returns different values according to how a certain condition is met. It is composed by applying a conditional function construct, of which Firebird supports several. This section describes only one conditional expression construct: CASE. All other conditional expressions apply internal functions derived from CASE and are described in Conditional Functions. The CASE construct returns a single value from a number of possible ones. Two syntactic variants are supported:. When this variant is used, test-expr is compared expr 1, expr 2 etc. If no match is found, defaultresult from the optional ELSE clause is returned. The returned result does not have to be a literal value: it might be a field or variable name, compound expression or NULL literal. The first expression to return TRUE determines the result. NULL is not a value in SQL, but a state indicating that the value of the element either is unknown or it does not exist. When you use NULL in logical Boolean expressions, the result will depend on the type of the operation and on other participating values. When you compare a value to NULL , the result will be unknown. Up to and including Firebird 2. However, there are logical expressions predicates that can return true, false or unknown. A subquery is a special form of expression that is actually a query embedded within another query. Subquery expressions can be used in the following ways:. To produce a set that the enclosing query can select from, as though were a regular table or view. A subquery can be correlated. A query is correlated when the subquery and the main query are interdependent. To process each record in the subquery, it is necessary to fetch a record in the main query; i. When subqueries are used to get the values of the output column in the SELECT list, a subquery must return a scalar result. Subqueries used in search predicates, other than existential and quantified predicates, must return a scalar result; that is, not more than one column from not more than one matching row or aggregation. Although it is reporting a genuine error, the message can be slightly misleading. Parentheses may be used for grouping predicates and controlling evaluation order. A predicate may embed other predicates. Evaluation sequence is in the outward direction, i. A comparison predicate consists of two expressions connected with a comparison operator. There are six traditional comparison operators:. For the complete list of comparison operators with their variant forms, see Comparison Operators. On the other hand, ptrtype can be tested for NULL and return a result: it is just that it is not a comparison test:. The search is inclusive the values represented by both arguments are included in the search. The LIKE predicate compares the character-type expression with the pattern defined in the second expression. Case- or accent-sensitivity for the comparison is determined by the collation that is in use. A collation can be specified for either operand, if required. If the tested value matches the pattern, taking into account wildcard symbols, the predicate is TRUE. If the search string contains either of the wildcard symbols, the ESCAPE clause can be used to specify an escape character. Actually, the LIKE predicate does not use an index. Search for tables containing the underscore character in their names. The search is case-sensitive. It can be used for an alphanumeric string-like search on numbers and dates. However, if an accent-sensitive collation is in use then the search will be accent-sensitive. Search for changes in salaries with the date containing number 84 in this case, it means changes that took place in :. The following syntax defines the SQL regular expression format. It is a complete and correct top-down definition. Feel free to skip it and read the next section, Building Regular Expressions , which uses a bottom-up approach, aimed at the rest of us. Within regular expressions, most characters represent themselves. The only exceptions are the special characters below:. A regular expression that contains no special or escape characters matches only strings that are identical to itself subject to the collation in use. A bunch of characters enclosed in brackets define a character class. A character in the string matches a class in the pattern if the character is a member of the class:. Within a class definition, two characters connected by a hyphen define a range. A range comprises the two endpoints and all the characters that lie between them in the active collation. Ranges can be placed anywhere in the class definition without special delimiters to keep them apart from the other elements. Latin letters a.. With an accent-insensitive collation, this class also matches accented forms of these characters. Uppercase Latin letters A.. Also matches lowercase with case-insensitive collation and accented forms with accent-insensitive collation. Lowercase Latin letters a.. Also matches uppercase with case-insensitive collation and accented forms with accent-insensitive collation. Including a predefined class has the same effect as including all its members. Predefined classes are only allowed within class definitions. If you need to match against a predefined class and nothing more, place an extra pair of brackets around it. If a class definition starts with a caret, everything that follows is excluded from the class. All other characters match:. If the caret is not placed at the start of the sequence, the class contains everything before the caret, except for the elements that also occur after the caret:. If the braces contain two numbers separated by a comma, the second number not smaller than the first, then the item must be repeated at least the first number and at most the second number of times in order to match:. A match is made when the argument string matches at least one of the terms:. A subexpression is a regular expression in its own right. It can contain all the elements allowed in a regular expression, and can also have quantifiers added to it. In order to match against a character that is special in regular expressions, that character has to be escaped. There is no default escape character; rather, the user specifies one when needed:. Since NULL is not a value, these operators are not comparison operators. In Firebird 3. This group of predicates includes those that use subqueries to submit values for all kinds of assertions in search conditions. Existential predicates are so called because they use various methods to test for the existence or non-existence of some assertion, returning TRUE if the existence or non-existence is confirmed or FALSE otherwise. The IN predicate tests whether the value of the expression on the left side is present in the set of values specified on the right side. The set of values cannot have more than items. The IN predicate can be replaced with the following equivalent forms:. When the IN predicate is used in the search conditions of DML queries, the Firebird optimizer can use an index on the searched column, if a suitable one exists. For instance, the following query:. The subquery may list several output columns since the rows are not returned anyway. They are only tested for singular existence. A quantifier is a logical operator that sets the number of objects for which this assertion is true. It is not a numeric quantity, but a logical one that connects the assertion with the full set of possible objects. Such predicates are based on logical universal and existential quantifiers that are recognised in formal logic. In subquery expressions, quantified predicates make it possible to compare separate values with the results of subqueries; they have the following common form:. When the ALL quantifier is used, the predicate is TRUE if every value returned by the subquery satisfies the condition in the predicate of the main query. If the subquery returns an empty set, the predicate is TRUE for every left-side value, regardless of the operator. This may appear to be contradictory, because every left-side value will thus be considered both smaller and greater than, both equal to and unequal to, every element of the right-side stream. Nevertheless, it aligns perfectly with formal logic: if the set is empty, the predicate is true 0 times, i. Apparently, both are present in the SQL standard so that they could be used interchangeably in order to improve the readability of operators. DDL statements are used to create, modify and delete database objects that have been created by users. When a DDL statement is committed, the metadata for the object are created, changed or deleted. This section describes how to create a database, connect to an existing database, alter the file structure of a database and how to delete one. Optionally includes a port number or service name. Full path and file name including its extension. The file name must be specified according to the rules of the platform file system being used. Database alias previously created in the aliases. User name of the owner of the new database. It may consist of up to 31 characters. Password of the user name as the database owner. The maximum length is 31 characters; however only the first 8 characters are considered. Page size for the database, in bytes. Possible values are the default , and Specifies the character set of the connection available to a client connecting after the database is successfully created. Single quotes are required. They are synonymous. A database may consist of one or several files. The first main file is called the primary file , subsequent files are called secondary file[s]. Nowadays, multi-file databases are considered an anachronism. It made sense to use multi-file databases on old file systems where the size of any file is limited. The primary file specification is the name of the database file and its extension with the full path to it according to the rules of the OS platform file system being used. The database file must not exist at the moment when the database is being created. If it does exist, you will get an error message and the database will not be created. If the full path to the database is not specified, the database will be created in one of the system directories. The particular directory depends on the operating system. For this reason, unless you have a strong reason to prefer that situation, always specify the absolute path, when creating either the database or an alias for it. You can use aliases instead of the full path to the primary database file. If you create a database on a remote server, you should specify the remote server specification. The remote server specification depends on the protocol being used. If you use the Named Pipes protocol to create a database on a Windows server, the primary file specification should look like this:. Clauses for specifying the user name and the password, respectively, of an existing user in the security database security2. The user specified in the process of creating the database will be its owner. This will be important when considering database and object privileges. Clause for specifying the database page size. This size will be set for the primary file and all secondary files of the database. If you specify the database page size less than 4,, it will be changed automatically to the default page size, 4, Other values not equal to either 4,, 8, or 16, will be changed to the closest smaller supported value. If the database page size is not specified, it is set to the default value of 4, Clause specifying the maximum size of the primary or secondary database file, in pages. When a database is created, its primary and secondary files will occupy the minimum number of pages necessary to store the system data, regardless of the value specified in the LENGTH clause. The file will keep increasing its size automatically when necessary. Clause specifying the character set of the connection available after the database is successfully created. The character set NONE is used by default. Notice that the character set should be enclosed in a pair of apostrophes single quotes. Clause specifying the default character set for creating data structures of string data types. The default will be used for the entire database except where an alternative character set, with or without a specified collation, is used explicitly for a field, domain, variable, cast expression, etc. Clause that specifies the database page number at which the next secondary database file should start. When the previous file is completely filled with data according to the specified page number, the system will start adding new data to the next database file. Databases are created in Dialect 3 by default. Creating a database in Windows, located on disk D with a page size of 8, The owner of the database will be the user wizard. The database will be in Dialect 1 and it will use WIN as its default character set. Creating a database in the Linux operating system with a page size of 4, The database will be in Dialect 3 and will use UTF8 as its default character set. Creating a database in Dialect 3 with UTF8 as its default character set. The primary file will contain up to 10, pages with a page size of 8, As soon as the primary file has reached the maximum number of pages, Firebird will start allocating pages to the secondary file test. If that file is filled up to its maximum as well, test. As the last file, it has no page limit imposed on it by Firebird. New allocations will continue for as long as the file system allows it or until the storage device runs out of free space. As far as file size and the use of secondary files are concerned, this database will behave exactly like the one in the previous example. The statement was documented incorrectly in the old InterBase 6 Language Reference. Adds a secondary file to the database. It is necessary to specify the full path to the file and the name of the secondary file. This clause does not actually add any file. It just overrides the default name and path of the. To change the existing settings, you should delete the previously specified description of the. If the path and name of the. If only a file name is specified, the. This is the clause that deletes the description path and name of the. The file is not actually deleted. Until the backup state of the database is reverted to NORMAL , all changes made to the database will be written to the. Despite its syntax, a statement with the BEGIN BACKUP clause does not start a backup process but just creates the conditions for doing a task that requires the database file to be read-only temporarily. A statement with this clause merges the. Use this method only on single-file databases. Adding a secondary file to the database. As soon as pages are filled in the previous primary or secondary file, the Firebird engine will start adding data to the secondary file test4. Before deleting a database, you have to connect to it. The statement deletes the primary file, all secondary files and all shadow files. A shadow is an exact, page-by-page copy of a database. Once a shadow is created, all changes made in the database are immediately reflected in the shadow. If the primary database file becomes unavailable for some reason, the DBMS will switch to the shadow. The name of the shadow file and the path to it, in accord with the rules of the operating system. The shadow starts duplicating the database right at the moment it is created. It is not possible for a user to connect to a shadow. Like a database, a shadow may be multi-file. The page size for shadow files is set to be equal to the database page size and cannot be changed. If a calamity occurs involving the original database, the system converts the shadow to a copy of the database and switches to it. The shadow is then unavailable. What happens next depends on the MODE option. When a shadow is converted to a database, it becomes unavailable. A shadow might alternatively become unavailable because someone accidentally deletes its file, or the disk space where the shadow files are stored is exhausted or is itself damaged. If the AUTO mode is selected the default value , shadowing ceases automatically, all references to it are deleted from the database header and the database continues functioning normally. It does not always succeed, however, and a new one may need to be created manually. If the MANUAL mode attribute is set when the shadow becomes unavailable, all attempts to connect to the database and to query it will produce error messages. MANUAL should be selected if continuous shadowing is more important than uninterrupted operation of the database. Clause specifying the maximum size of the primary or secondary shadow file in pages. The last or only file will keep automatically increasing in size as long as it is necessary. Clause specifying the shadow page number at which the next shadow file should start. The system will start adding new data to the next shadow file when the previous file is filled with data up to the specified page number. A domain is created as a specific data type with some attributes attached to it. Those objects inherit all of the attributes of the domain. Some attributes can be overridden when the new object is defined, if required. This section describes the syntax of statements used to create, modify and delete domains. The total number of significant digits that a value of the datatype can hold The name of a valid character set, if the character set of the domain is to be different to the default character set of the database. The dimensions of the array are specified between square brackets. In the Syntax block, these brackets appear in quotes to distinguish them from the square brackets that identify optional syntax elements. For each array dimension, one or two integer numbers define the lower and upper boundaries of its index range:. By default, arrays are 1-based. The lower boundary is implicit and only the upper boundary need be specified. A single number smaller than 1 defines the range num.. One or both boundaries can be less than zero, as long as the upper boundary is greater than the lower. When the array has multiple dimensions, the range definitions for each dimension must be separated by commas and optional whitespace. Subscripts are validated only if an array actually exists. It means that no error messages regarding invalid subscripts will be returned if selecting a specific element returns nothing or if an array field is NULL. If no character set was specified then, the character set NONE is applied by default when you create a character domain. With character set NONE , character data are stored and retrieved the way they were submitted. Data in any encoding can be added to a column based on such a domain, but it is impossible to add this data to a column with a different encoding. Because no transliteration is performed between the source and destination encodings, errors may result. Local variables and arguments in PSQL modules that reference this domain will be initialized with the default value. For the default value, use a literal of a compatible type or a context variable of a compatible type. When creating a domain, take care to avoid specifying limitations that would contradict one another. A domain constraint specifies conditions that must be satisfied by the values of table columns or variables that inherit from the domain. A condition must be enclosed in parentheses. It contains the value assigned to the variable or the table column. If no collation sequence is specified, the collation sequence will be the one that is default for the specified character set at the time the domain is created. Creating a domain that can take the values 'Yes' and 'No' in the default character set specified during the creation of the database. The starting array index is 1. Domains defined over an array type may be used only to define table columns. You cannot use array domains to define local variables in PSQL modules. The example is given only to show the possibility of using predicates with queries in the domain test condition. It is not recommended to create this style of domain in practice unless the lookup table contains data that are never deleted. The name of a valid character set, if the character set of the domain is to be changed. Use the TO clause to rename the domain, as long as there are no dependencies on the domain, i. Use this clause to delete a previously specified default value and replace it with NULL. The TYPE clause is used to change the data type of the domain to a different, compatible one. The system will forbid any change to the type that could result in data loss. An example would be if the number of characters in the new type were smaller than in the existing type. When you alter the attributes of a domain, existing PSQL code may become invalid. Any user connected to the database can alter a domain, provided it is not prevented by dependencies from objects to which that user does not have sufficient privileges. If the domain was declared as an array, it is not possible to change its type or its dimensions; nor can any other type be changed to an ARRAY type. In Firebird 2. There is no way to change the default collation without dropping the domain and recreating it with the desired attributes. It is not possible to delete a domain if it is referenced by any database table columns or used in any PSQL module. In order to delete a domain that is in use, all columns in all tables that refer to the domain will have to be dropped and all references to the domain will have to be removed from PSQL modules. A table is a flat, two-dimensional structure containing any number of rows. Table rows are often called records. All rows in a table have the same structure and consist of columns. Table columns are often called fields. A table must have at least one column. Each column contains a single type of SQL data. Name identifier for the table. It may consist of up to 31 characters and must be unique in the database. File specification only for external tables. Name identifier for a column in the table. May consist of up to 31 characters and must be unique in the table. The name of a valid character set, if the character set of the column is to be different to the default character set of the database. Any user can create it and its name must be unique among the names of all tables, views and stored procedures in the database. A table must contain at least one column that is not computed and the names of columns must be unique in the table. In Firebird, columns are nullable by default. If the character set is not specified, the character set specified during the creation of the database will be used by default. If no character set was specified during the creation of the database, the NONE character set is applied by default. In this case, data is stored and retrieved the way it was submitted. Data in any encoding can be added to such a column, but it is not possible to add this data to a column with a different encoding. No transliteration is performed between the source and destination encodings, which may result in errors. If no collation sequence is specified, the collation sequence that is default for the specified character set during the creation of the column is applied by default. The default value can be a literal of a compatible type, a context variable that is type-compatible with the data type of the column, or NULL , if the column allows it. If no default value is explicitly specified, NULL is implied. To define a column, you can use a previously defined domain. If you want to have a domain that might be used for defining both nullable and non-nullable columns and variables, it is better practice to make the domain nullable and apply NOT NULL in the downstream column definitions and variable declarations. They mean the same. Describing the data type is not required but possible for calculated fields, as the DBMS calculates and stores the appropriate type as a result of the expression analysis. Appropriate operations for the data types included in an expression must be specified precisely. If the data type is explicitly specified for a calculated field, the calculation result is converted to the specified type. This means, for instance, that the result of a numeric expression could be rendered as a string. Instead of a computed column, in some cases it makes sense to use a regular column whose value is evaluated in triggers for adding and updating data. In the Syntax block these brackets appear in quotes to distinguish them from the square brackets that identify optional syntax elements. Table-level constraints are needed when keys uniqueness constraint, Primary Key, Foreign Key are to be formed across multiple columns and when a CHECK constraint involves other columns in the row besides the column being defined. Syntax for some types of constraint may differ slightly according to whether the constraint is being defined at column or table level. A column-level constraint is specified during a column definition, after all column attributes except COLLATION are specified, and can involve only the column specified in that definition. Table-level constraints are specified after all of the column definitions. They are a more flexible way to set constraints, since they can cater for constraints involving multiple columns. Again, n represents one or more digits. Automatic naming of table-level constraints and their indexes follows the same pattern, unless the names are supplied explicitly. By default, the constraint index will have the same name as the constraint. The values across the key columns in any row must be unique. A table can have only one primary key. A table can contain any number of unique key constraints. As with the Primary Key, the Unique constraint can be multi-column. If so, it must be specified as a table-level constraint. Multiple rows having the same key columns null and the rest filled with non-null values are allowed, provided the values differ in at least one column. Multiple rows having the same key columns null and the rest filled with non-null values that are the same in every column will violate the constraint. A Foreign Key ensures that the participating column s can contain only values that also exist in the referenced column s in the master table. These referenced columns are often called target columns. They must be the primary key or a unique key in the target table. They need not have a NOT NULL constraint defined on them although, if they are the primary key, they will, of course, have that constraint. Both single-column and multi-column foreign keys can be defined at the table level. For a multi-column Foreign Key, the table-level declaration is the only option. This method also enables the provision of an optional name for the constraint:. The change in the master table is propagated to the corresponding row s in the child table. If a key value changes, the corresponding key in the child records changes to the new value; if the master row is deleted, the child records are deleted. The Foreign Key columns in the affected rows will be set to their default values as they were when the foreign key constraint was defined. Such conditions will cause the operation on the master table to fail with an error message. The Firebird engine has no way, during definition, to verify that the extra CHECK does not conflict with the existing one. Global temporary tables have persistent metadata, but their contents are transaction-bound the default or connection-bound. Every transaction or connection has its own private instance of a GTT, isolated from all the others. Instances are only created if and when the GTT is referenced. They are destroyed when the transaction ends or on disconnection. Use this query to find out what type of table you are looking at:. A file that is defined as an external table must be located on a storage device that is physically present on the machine where the Firebird server runs and, if the parameter ExternalFileAccess in the firebird. If the file does not exist yet, Firebird will create it on first access. The ability to use external files for a table depends on the value set for the ExternalFileAccess parameter in firebird. If it is set to None the default , any attempt to access an external file will be denied. The Restrict setting is recommended, for restricting external file access to directories created explicitly for the purpose by the server administrator. For example:. Note that any path that is a network mapping will not work. Paths enclosed in single or double quotes will not work, either. If this parameter is set to Full , external files may be accessed anywhere on the host file system. It creates a security vulnerability and is not recommended. There are no field delimiters: both field and row boundaries are determined by maximum sizes, in bytes, of the field definitions. It is important to keep this in mind, both when defining the structure of the external table and when designing an input file for an external table that is to import data from another application. The most useful data type for the columns of external tables is the fixed-length CHAR type, of suitable lengths for the data they are to carry. Of course, there are ways to manipulate typed data so as to generate output files from Firebird that can be read directly as input files to other applications, using stored procedures, with or without employing external tables. Such techniques are beyond the scope of a language reference. Here, we provide some guidelines and tips for producing and working with simple text files, since the external table feature is often used as an easy way to produce or read transaction-independent logs that can be studied off-line in a text editor or auditing application. There are various ways to populate this delimiter column. For our example, we will define an external log table that might be used by an exception handler in a stored procedure or trigger. The external table is chosen because the messages from any handled exceptions will be retained in the log, even if the transaction that launched the process is eventually rolled back because of another, unhandled exception. For demonstration purposes, it has just two data columns, a time stamp and a message. The third column stores the row delimiter:. Now, a trigger, to write the timestamp and the row delimiter each time a message is written to the file:. Inserting some records which could have been done by an exception handler or a fan of Shakespeare :. Creating the STOCK table with the named primary key specified at the column level and the named unique key specified at the table level. The table also contains an array of 5 elements. The first one is declared according to the SQL standard, while the second one is declared according to the traditional declaration of computed fields in Firebird. Creating a transaction-scoped global temporary table that uses a foreign key to reference a connection-scoped global temporary table. Name identifier for a column in the table, max. Must be unique in the table. New name identifier for the column, max. The new column position an integer between 1 and the number of columns in the table. The number of metadata changes is limited to for each table. Once the counter reaches the limit, you will not be able to make any further changes to the structure of the table without resetting the counter. With the ADD clause you can add a new column or a new table constraint. It may lead to breaking the logical integrity of data, since you will have existing records containing NULL in a non-nullable column. When adding a non-nullable column, it is recommended either to set a default value for it or to update the column in existing rows with a non-null value. An attempt to drop a column will fail if anything references it. Consider the following items as sources of potential dependencies:. Deleting a column constraint or a table constraint does not increase the metadata change counter. Permitted modifications are:. The TO keyword with a new identifier renames an existing column. The table must not have an existing column that has the same identifier. Renaming a column will also be disallowed if the column is used in any trigger, stored procedure or view. The keyword TYPE changes the data type of an existing column to another, allowable type. A type change that might result in data loss will be disallowed. If the column was declared as an array, no change to its type or its number of dimensions is permitted. The data type of a column that is involved in a foreign key, primary key or unique constraint cannot be changed at all. If a position number is greater than the number of columns in the table, its new position will be adjusted silently to match the number of columns. If the column is based on a domain with a default value, the default value will revert to the domain default. An execution error will be raised if an attempt is made to delete the default value of a column which has no default value or whose default value is domain-based. If the column already has a default value, it will be replaced with the new one. The default value applied to a column always overrides one inherited from a domain. Converting a regular column to a computed one and vice versa are not permitted. When a table is dropped, all triggers for its events and indexes built for its fields will be deleted as well. Existing dependencies will prevent the statement from executing. An index is a database object used for faster data retrieval from a table or for speeding up the sorting of query. This section describes how to create indexes, activate and deactivate them, delete them and collect statistics recalculate selectivity for them. Name of a column in the table. Indexes are created automatically in the process of defining constraints, such as primary key, foreign key or unique constraints. An index can be built on the content of columns of any data type except for BLOB and arrays. The name identifier of an index must be unique among all index names. When a primary key, foreign key or unique constraint is added to a table or column, an index with the same name is created automatically, without an explicit directive from the designer. Specifying the keyword UNIQUE in the index creation statement creates an index in which uniqueness will be enforced throughout the table. A unique index is not a constraint. Unique indexes cannot contain duplicate key values or duplicate key value combinations, in the case of compound , or multi-column, or multi-segment indexes. All indexes in Firebird are uni-directional. An index may be constructed from the lowest value to the highest ascending order or from the highest value to the lowest descending order. It is quite valid to define both an ascending and a descending index on the same column or key set. The expression in a computed index may involve several columns in the table. The number of indexes that can be accommodated for each table is limited. The actual maximum for a specific table depends on the page size and the number of columns in the indexes. The maximum indexed string length is 9 bytes less than the maximum key length. The maximum indexable string length depends on the page size and the character set. There is no facility on this statement for altering any attributes of the index. Altering a constraint index to the inactive state is not permitted. Activating an inactive index is also safe. If the transaction is in WAIT mode, it will wait for completion of concurrent transactions. It might be useful to switch an index to the inactive state whilst inserting, updating or deleting a large batch of records in the table that owns the index. With the ACTIVE option, if the index is in the inactive state, it will be switched to active state and the system rebuilds the index. Rebuilding indexes can be a useful piece of houskeeping to do, occasionally, on the indexes of a large table in a database that has frequent inserts, updates or deletes but is infrequently restored. The selectivity of an index is the result of evaluating the number of rows that can be selected in a search on every index value. A unique index has the maximum selectivity because it is impossible to select more than one row for each value of an index key if it is used. Index statistics in Firebird are not automatically recalculated in response to large batches of inserts, updates or deletions. It may be beneficial to recalculate the selectivity of an index after such operations because the selectivity tends to become outdated. The selectivity of an index can be recalculated by the owner of the table or an administrator. It can be performed under concurrent load without risk of corruption. Data can be retrieved from one or more tables, from other views and also from selectable stored procedures. Unlike regular tables in relational databases, a view is not an independent data set stored in the database. The result is dynamically created as a data set when the view is selected. The metadata of a view are available to the process that generates the binary code for stored procedures and triggers, just as though they were concrete tables storing persistent data. The identifier name of a view must be unique among the names of all views, tables and stored procedures in the database. The name of the new view can be followed by the list of column names that should be returned to the caller when the view is invoked. Names in the list do not have to be related to the names of the columns in the base tables from which they derive. If duplicate names or non-aliased expression-derived columns make this impossible to obtain a valid list, creation of the view fails with an error. If the full list of columns is specified, it makes no sense to specify aliases in the SELECT statement because the names in the column list will override them. The column list is optional if all the columns in the SELECT are explicitly named and are unique in the selection list. A view can be updatable or read-only. Changes made in an updatable view are applied to the underlying table s. A read-only view can be made updateable with the use of triggers. Once triggers have been defined on a view, changes posted to it will never be written automatically to the underlying table, even if the view was updateable to begin with. It is the responsibility of the programmer to ensure that the triggers update or delete from, or insert into the base tables as needed. Every attempt to insert a new record or to update an existing one is checked whether the new or updated record would meet the WHERE criteria. If they fail the check, the operation is not performed and an appropriate error message is returned. An error message is returned otherwise. Therefore, if the check on the input fails, any default clauses or triggers on the base relation that might have been designed to correct the input will never come into action. As a result, base table defaults defined on such fields will not be applied. Triggers, on the other hand, will fire and work as expected. It will always be the case if the view owner is also the owner of the underlying objects. Privileges for views remain intact and dependencies are not affected. Be careful when you change the number of columns in a view. Existing application code and PSQL modules that access the view may become invalid. Privileges for an existing view remain intact and dependencies are not affected. The statement will fail if the view has dependencies. Creates or recreates a view. If there is a view with this name already, the engine will try to drop it before creating the new instance. A trigger is a special type of stored procedure that is not called directly, instead being executed when a specified event occurs in the associated table or view. It can be specified to execute for one specific event insert, update, delete or for some combination of two or three of those events. Trigger name consisting of up to 31 characters. It must be unique among all trigger names in the database. A trigger can be created either for a relation table view event or a combination of events , or for a database event. The header specifies the name of the trigger, the name of the relation for a relation trigger , the phase of the trigger and the event[s] it applies to. The body consists of optional declarations of local variables and named cursors followed by one or more statements, or blocks of statements, all enclosed in an outer block that begins with the keyword BEGIN and ends with the keyword END. This creates a conflict with PSQL syntax when coding in these environments. If you are unacquainted with this problem and its solution, please study the details in the PSQL chapter in the section entitled Switching the Terminator in isql. Relation triggers are executed at the row record level every time the row image changes. Only active triggers are executed. Phase concerns the timing of the trigger with regard to the change-of-state event in the row of data:. If multiple operations are specified, they must be separated by the keyword OR. No operation may occur more than once. The default position is 0. If no positions are specified, or if several triggers have a single position number, the triggers will be executed in the alphabetical order of their names. The optional declarations section beneath the keyword AS in the header of the trigger is for defining variables and named cursors that are local to the trigger. If all goes well, the transaction is committed. Uncaught exceptions cause the transaction to roll back, and. The connection is broken as intended. The action taken after an uncaught exception depends on the event:. Both phenomena effectively lock you out of your database until you get in there with database triggers suppressed and fix the bad code. Some Firebird command-line tools have been supplied with switches that an administrator can use to suppress the automatic firing of database triggers. So far, they are:. Only the database owner and administrators have the authority to create database triggers. Creating a trigger for the event of connecting to the database that logs users logging into the system. The trigger is created as inactive. Creating a trigger for the event of connecting to the database that does not permit any users, except for SYSDBA, to log in during off hours. Events; but relation trigger events cannot be changed to database trigger events, nor vice versa. The events should be separated with the keyword OR. No event should be mentioned more than once. A stored procedure is a software module that can be called from a client, another procedure, an executable block or a trigger. Among notable exceptions are DDL and transaction control statements. Stored procedure name consisting of up to 31 characters. Must be unique among all table, view and procedure names in the database. A literal value that is assignment-compatible with the data type of the parameter. Any context variable whose type is compatible with the data type of the parameter. The name of an input or output parameter of the procedure. The name of the parameter must be unique among input and output parameters of the procedure and its local variables. The total number of significant digits that the parameter should be able to hold The name of the procedure must be unique among the names of all stored procedures, tables and views in the database. The header specifies the name of the procedure and declares input parameters and the output parameters, if any, that are to be returned by the procedure. The procedure body consists of declarations for any local variables and named cursors that will be used by the procedure, followed by one or more statements, or blocks of statements, all enclosed in an outer block that begins with the keyword BEGIN and ends with the keyword END. Each parameter has a data type specified for it. Input parameters are presented as a parenthesized list following the name of the procedure. They are passed into the procedure as values, so anything that changes them inside the procedure has no effect on the parameters in the calling program. Input parameters may have default values. Those that do have values specified for them must be located at the end of the list of parameters. A domain name can be specified as the type of a parameter. The parameter will inherit all domain attributes. If a default value is specified for the parameter, it overrides the default value specified in the domain definition. However, if the domain is of a text type, its character set and collation sequence are always used. Input and output parameters can also be declared using the data type of columns in existing tables and views. The constraints and default value of the column are ignored. For local variables, the behaviour varies. The optional declarations section, located last in the header section of the procedure definition, defines variables local to the procedure and its named cursors. Local variable declarations follow the same rules as parameters regarding specification of the data type. Any user connected to the database can create a new stored procedure. The user who creates a stored procedure becomes its owner. Creating a stored procedure that inserts a record into the BREED table and returns the code of the inserted record:. Creating a selectable stored procedure that generates data for mailing labels from employee. Take care about changing the number and type of input and output parameters in stored procedures. Existing application code and procedures and triggers that call it could become invalid because the new description of the parameters is incompatible with the old calling format. If the procedure already exists, it will be altered and compiled without affecting its existing privileges and dependencies. If the stored procedure has any dependencies, the attempt to delete it will fail and the appropriate error will be raised. If there is a procedure with this name already, the engine will try to delete it and create a new one. After a procedure is successfully recreated, privileges to execute the stored procedure and the privileges of the stored procedure itself are dropped. All sections from this point forward to the end of the chapter are awaiting technical and editorial review. Once declared to a database, they become available in dynamic and procedural statements as though they were implemented in the SQL language internally. External functions extend the possibilities for processing data with SQL considerably. Function name in the database. The number of the input parameter, numbered from 1 in the list of input parameters in the declaration, describing the data type that will be returned by the function. UDF declarations must be made in each database that is going to use them. There is no need to declare UDFs that will never be used. The name of the external function must be unique among all function names. The input parameters of the function follow the name of the function and are separated with commas. Each parameter has an SQL data type specified for it. Arrays cannot be used as function parameters. By default, input parameters are passed by reference. Passing a parameter by descriptor makes it possible to process NULLs. Required specifies the output parameter returned by the function. A function is scalar: it returns one and only one parameter. The output parameter can be passed by reference the default , by descriptor or by value. It is necessary if you need to return a value of data type BLOB. It is used only if the memory was allocated dynamically in the UDF. The link to the module should not be the full path and extension of the file, if that can be avoided. If the module is located in the default location in the.. The UDFAccess parameter in the firebird. Declaring the addDay external function located in the fbudf module. The input and output parameters are passed by reference. Declaring the invl external function located in the fbudf module. The input and output parameters are passed by descriptor. Declaring the isLeapYear external function located in the fbudf module. The input parameter is passed by reference, while the output parameter is passed by value. Declaring the i64Truncate external function located in the fbudf module. The second parameter of the function is used as the return value. Existing dependencies remain intact after the statement containing the change[s] is executed. If there are any dependencies on the external function, the statement will fail and the appropriate error will be raised. External functions for converting BLOB types are stored in dynamic libraries and loaded when necessary. Filter name in the database. The subtypes can be specified as the subtype number or as the subtype mnemonic name. Custom subtypes must be represented by negative numbers from -1 to , An attempt to declare more than one BLOB filter with the same combination of the input and output types will fail with an error. After the transaction is committed, the mnemonic names can be used in declarations when you create new filters. If mnemonic names in upper case, they can be used case-insensitively and without quotation marks when a filter is declared. From Firebird 3 onward, the system tables will no longer be writable by users. The clause defining the name of the module where the exported function is located. By default, modules must be located in the UDF folder of the root directory on the server. The UDFAccess parameter in firebird. Removing a BLOB filter from a database makes it unavailable for use from that database. The dynamic library where the conversion function is located remains intact and the removal from one database does not affect other databases in which the same BLOB filter is still declared. A sequence or a generator is a database object used to get unique number values to fill a series. Both terms are implemented in Firebird, which recognises and has syntax for both terms. Sequences or generators are always stored as bit integers, regardless of the SQL dialect of the database. If a client is connected using Dialect 1, the server sends sequence values to it as bit integers. Passing a sequence value to a bit field or variable will not cause errors as long as the current value of the sequence does not exceed the limits of a bit number. However, as soon as the sequence value exceeds this limit, a database in Dialect 3 will produce an error. A database in Dialect 1 will keep cutting the values, which will compromise the uniqueness of the series. When a sequence is created, its value is set to 0. New sequence generator value. A bit integer from -2 to 2 63 This section describes how to create, modify and delete custom exceptions for use in error handlers in PSQL modules. If an exception of the same name exists, the statement will fail with an appropriate error message. The exception name is a standard identifier. In a Dialect 3 database, it can be enclosed in double quotes to make it case-sensitive and, if required, to use characters that are not valid in regular identifiers. See Identifiers for more information. The default message is stored in character set NONE , i. The text can be overridden in the PSQL code when the exception is thrown. A system of prefixes for naming and categorising groups of exceptions is recommended. Any user connected to the database can alter an exception message. Modifying the message returned from a custom exception, if the exception exists; otherwise, creating a new exception. If an existing exception is altered by this statement, any existing dependencies will remain intact. Any user connected to the database can use this statement to create an exception or alter the text of one that already exists. Any dependencies on the exception will cause the statement to fail and the exception will not be deleted. If an exception is used only in stored procedures, it can be deleted at any time. If it is used in a trigger, it cannot be deleted. In planning to delete an exception, all references to it should first be removed from the code of stored procedures, to avoid its absence causing errors. The collation must already be present on the system, typically in a library file, and must be properly registered in a. The collname , charset and basecoll parameters are case-insensitive unless enclosed in double-quotes. The available specific attributes are listed in the table below. Not all specific attributes apply to every collation, even if specifying them does not cause an error. Disables compressions a. Compressions cause certain character sequences to be sorted as atomic units, e. Disables expansions. Expansions cause certain characters e. Specifies the ICU library version to use. Specifies the collation locale. Requires complete version of ICU libraries. Treats contiguous groups of decimal digits in the string as atomic units and sorts them numerically. This is also known as natural sorting. Orders special characters spaces, symbols etc. In order for this to work, the character set must be present on the system and registered in a. Creating a case-insensitive collation based on one already existing in the database with specific attributes. An error will be raised if the specified collation is not present. In that case, the collation sequence of existing domains, columns and PSQL variables will remain intact after the change to the default collation of the underlying character set. If you change the default collation for the database character set the one defined when the database was created , it will change the default collation for the database. A role is a database object that packages a set of SQL privileges. Roles implement the concept of access control at a group level. Multiple privileges are granted to the role and then that role can be granted to or revoked from one or many users. A user that is granted a role must supply that role in his login credentials in order to exercise the associated privileges. Any other privileges granted to the user are not affected by his login with the role. Logging in with multiple roles simultaneously is not supported. The name of a role must be unique among the names of roles in the current database. It is advisable to make the name of a role unique among user names as well. The system will not prevent the creation of a role whose name clashes with an existing user name but, if it happens, the user will be unable to connect to the database. Any user connected to the database can create a role. The user that creates a role becomes its owner. Its actual effect is to alter an attribute of the database: Firebird uses it to enable and disable the capability for Windows Adminstrators to assume administrator privileges automatically when logging in. Several factors are involved in enabling this feature. It takes just a single argument, the name of the role. Once the role is deleted, the entire set of privileges is revoked from all users and objects that were granted the role. A role can be deleted by its owner or by an administrator. Database objects and a database itself may contain comments. It is a convenient mechanism for documenting the development and maintenance of a database. Client applications can view comments from these fields. Data are returned in zero or more rows , each containing one or more columns or fields. The total of rows returned is the result set of the statement. This part specifies what you want to retrieve. The FROM keyword, followed by a selectable object. This tells the engine where you want to get it from. The column list may contain all kinds of expressions instead of just column names, and the source need not be a table or view: it may also be a derived table, a common table expression CTE or a selectable stored procedure SP. Query parameter place-holder. You are advised to use the ROWS syntax wherever possible. FIRST limits the output of a query to the first m rows. SKIP will suppress the given n rows before starting to return output. This implies that a subquery expression must be enclosed in two pairs of parentheses. If the number of rows in the dataset or the remainder left after a SKIP is less than the value of the m argument supplied for FIRST , that smaller number of rows is returned. These are valid results, not error conditions. The subquery retrieves 10 rows each time, deletes them and the operation is repeated until the table is empty. Keep it in mind! The columns list contains one or more comma-separated value expressions. Each expression provides a value for one output column. Only for character-type columns: a collation name that exists and is valid for the character set of the data. For example, relationname. Qualifying is required if the column name occurs in more than one relation taking part in a join. Aliases obfuscate the original relation name: once a table, view or procedure has been aliased, only the alias can be used as its qualifier throughout the query. The relation name itself becomes unavailable. That is, if two or more rows have the same values in every corresponding column, only one of them is included in the result set. ALL is the default: it returns all of the rows, including duplicates. However, if the specified collation changes the case or accent sensitivity of the column, it may influence:. This query uses a CASE construct to determine the correct title, e. Selecting from columns of a derived table. A derived table is a parenthesized SELECT statement whose result set is used in an enclosing query as if it were a regular table or view. The derived table is shown in bold here:. Another example is:. The FROM clause specifies the source s from which the data are to be retrieved. In its simplest form, this is just a single table or view. But the source can also be a selectable stored procedure, a derived table or a common table expression. Multiple sources can be combined using various types of joins. This section concentrates on single-source selects. Joins are discussed in a following section. When selecting from a single table or view, the FROM clause need not contain anything more than the name. The output parameters of a selectable stored procedure correspond to the columns of a regular table. Selecting from a stored procedure without input parameters is just like selecting from a table or view:. Any required input parameters must be specified after the procedure name, enclosed in parentheses:. Values for optional parameters that is, parameters for which default values have been defined may be omitted or provided. However, if you provide them only partly, the parameters you omit must all be at the tail end. The result set of the statement acts as a virtual table which the enclosing statement can query. The derived table in the query below returns the list of table names in the database and the number of columns in each. A trivial example demonstrating how the alias of a derived table and the list of column aliases both optional can be used:. Each column in a derived table must have a name. The list of column aliases is optional but, if it exists, it must contain an alias for every column in the derived table. The optimizer can process derived tables very effectively. However, if a derived table is included in an inner join and contains a subquery, the optimizer will be unable to use any join order. It has been defined like this:. Depending on the values of a , b and c , each equation may have zero, one or two solutions. It is possible to find these solutions with a single-level query on table COEFFS , but the code will look rather messy and several values like the discriminant will have to be calculated multiple times per row. A derived table can help keep things clean here:. If we want to show the coefficients next to the solutions which may not be a bad idea , we can alter the query like this:. Notice that whereas the first query used a column aliases list for the derived table, the second adds aliases internally where needed. Both methods work, as long as every column is guaranteed to have a name. A common table expression or CTE is a more complex variant of the derived table, but it is also more powerful. The main query, which follows the preamble, can then access these CTE 's as if they were regular tables or views. The CTE 's go out of scope once the main query has run to completion. But we can now also eliminate the double calculation of sqrt D for every row:. The code is a little more complicated now, but it might execute more efficiently depending on what takes more time: executing the SQRT function or passing the values of b , D and denom through an extra CTE. Incidentally, we could have done the same with derived tables, but that would involve nesting. Joins combine data from two sources into a single set. This is done on a row-by-row basis and usually involves checking a join condition in order to determine which rows should be merged and appear in the resulting dataset. A join always combines data rows from two sets usually referred to as the left set and the right set. By default, only rows that meet the join condition i. This default type of join is called an inner join. Suppose we have the following two tables:. The other rows from the source tables have no match in the opposite set and are therefore not included in the join. We can make that fact explicit by writing:. It is perfectly possible that a row in the left set matches several rows from the right set or vice versa. In that case, all those combinations are included, and we can get results like:. Sometimes we want or need all the rows of one or both of the sources to appear in the joined set, regardless of whether they match a record in the other source. This is where outer joins come in. A LEFT outer join includes all the records from the left set, but only matching records from the right set. FULL outer joins include all the records from both sets. Below are the results of the various outer joins when applied to our original tables A and B :. Qualified joins specify conditions for the combining of rows. Most qualified joins have an ON clause, with an explicit condition that can be any valid boolean expression but usually involves some comparison between the two sources involved. Joins like these are called equi-joins. The examples in the section on inner and outer joins were al equi-joins. Equi-joins often compare columns that have the same name in both tables. If this is the case, we can also use the second type of qualified join: the named columns join. So instead of this:. Obviously, they will have the same values. If you want all the columns in the result set of the named columns join, set up your query like this:. Whether this is a problem or not depends on the situation. This has the additional benefit that it forces you to think about which data you want to retrieve and where from. It is your responsibility to make sure that the column names in the USING list are of compatible types between the two sources. If the types are compatible but not equal, the engine converts them to the type with the broadest range of values before comparing the values. Qualified columns on the other hand will always retain their original data type. Taking the idea of the named columns join a step further, a natural join performs an automatic equi-join on all the columns that have the same name in the left and right table. The data types of these columns must be compatible. This operator returns true if the operands have the same value or if they are both NULL. A cross join produces the full set product of the two data sources. This means that it successfully matches every row in the left source to every row in the right source. Please notice that the comma syntax is deprecated! It is only supported to keep legacy code working and may disappear in some future version. Cross-joining two sets is equivalent to joining them on a tautology a condition that is always true. The following two statements have the same effect:. Cross joins are inner joins, because they only include matching records — it just so happens that every record matches! Cross joins are seldom useful, except if you want to list all the possible combinations of two or more variables. Suppose you are selling a product that comes in different sizes, different colors and different materials. If these variables are each listed in a table of their own, this query would return all the combinations:. Firebird rejects unqualified field names in a query if these field names exist in more than one dataset involved in a join. This is even true for inner equi-joins where the field name figures in the ON clause like this:. There is one exception to this rule: with named columns joins and natural joins, the unqualified field name of a column taking part in the matching process may be used legally and refers to the merged column of the same name. For natural joins, they are the columns that have the same name in both relations. In that case, the value in the merged, unqualified column may mask the fact that one of the source values is absent. If a join is performed with a stored procedure that is not correlated with other data streams via input parameters, there are no oddities. If correlation is involved, an unpleasant quirk reveals itself. The problem is that the optimizer denies itself any way to determine the interrelationships of the input parameters of the procedure from the fields in the other streams:. This quirk has been recognised as a bug in the optimizer and will be fixed in the next version of Firebird. The condition in the WHERE clause is often called the search condition , the search expression or simply the search. This is useful if a query has to be repeated a number of times with different input values. In the SQL string as it is passed to the server, question marks are used as placeholders for the parameters. They are called positional parameters because they can only be told apart by their position in the string. Connectivity libraries often support named parameters of the form :id , :amount , :a etc. These are more user-friendly; the library takes care of translating the named parameters to positional parameters before passing the statement to the server. Only those rows for which the search condition evaluates to TRUE are included in the result set.