Chapter 7. Procedural SQL (PSQL) Statements

Procedural SQL (PSQL) is a procedural extension of SQL. This language subset is used for writing stored procedures, triggers, and PSQL blocks.

PSQL provides all the basic constructs of traditional structured programming languages, and also includes DML statements (SELECT, INSERT, UPDATE, DELETE, etc.), with a slight modified syntax in some cases.

7.1 Elements of PSQL

A procedural extension may contain declarations of local variables, routines and cursors, assignments, conditional statements, loops, statements for raising custom exceptions, error handling and sending messages (events) to client applications. Triggers have access to special context variables, two arrays that store, respectively, the NEW values for all columns during insert and update activity, and the OLD values during update and delete work.

Statements that modify metadata (DDL) are not available in PSQL.

7.1.1 DML Statements with Parameters

If DML statements (SELECT, INSERT, UPDATE, DELETE, etc.) in the body of the module (procedure, function, trigger or block) use parameters, only named parameters can be used. If DML statements contain named parameters, then they must be previously declared as local variables using DECLARE [VARIABLE] in the declaration section of the module, or as input or output variables in the module header.

When a DML statement with parameters is included in PSQL code, the parameter name must be prefixed by a colon (:) in most situations. The colon is optional in statement syntax that is specific to PSQL, such as assignments and conditionals and the INTO clause. The colon prefix on parameters is not required when calling stored procedures from within another PSQL module or in DSQL.

7.1.2 Transactions

Stored procedures and functions (including those defined in packages) are executed in the context of the transaction in which they are called. Triggers are executed as an intrinsic part of the operation of the DML statement: thus, their execution is within the same transaction context as the statement itself. Individual transactions are launched for database event triggers.

Statements that start and end transactions are not available in PSQL, but it is possible to run a statement or a block of statements in an autonomous transaction.

7.1.3 Module Structure

PSQL code modules consist of a header and a body. The DDL statements for defining them are complex statements; that is, they consist of a single statement that encloses blocks of multiple statements. These statements begin with a verb (CREATE, ALTER, DROP, RECREATE, CREATE OR ALTER) and end with the last END statement of the body. The Module Header

The header provides the module name and defines any input and output parameters or — for functions — the return type. Stored procedures and PSQL blocks may have input and output parameters. Functions may have input parameters and must have a scalar return type. Triggers do not have either input or output parameters.

The header of a trigger indicates the database event (insert, update or delete, or a combination) and the phase of operation (BEFORE or AFTER that event) that will cause it to fire. The Module Body

The module body is either a PSQL module body, or an external module body.

Syntax of a Module Body

<module-body> ::=
  <psql-module-body> | <external-module-body>
<psql-module-body> ::=
<external-module-body> ::=
  EXTERNAL [NAME <extname>] ENGINE engine
  [AS '<extbody>']
<declarations> ::= <declare-item> [<declare-item ...]
<declare-item> ::=
  | <declare-cursor>
  | <declare-subfunc>
  | <declare-subproc>
<extname> ::=

Table Module Body Parameters


Section for declaring local variables, named cursors, and subroutines


Procedural SQL statements. Some PSQL statements may not be valid in all types of PSQL. For example, RETURN <value>; is only valid in functions.


Local variable declaration


Named cursor declaration


Sub-function declaration


Sub-procedure declaration


String identifying the external procedure


String identifying the UDR engine


External procedure body. A string literal that can be used by UDRs for various purposes.


The name of the module that contains the procedure


The internal name of the procedure inside the external module


Optional string that is passed to the procedure in the external module The PSQL Module Body

The PSQL body starts with an optional section that declares variables and subroutines, followed by a block of statements that run in a logical sequence, like a program. A block of statements — or compound statement — is enclosed by the BEGIN and END keywords, and is executed as a single unit of code. The main BEGIN…​END block may contain any number of other BEGIN…​END blocks, both embedded and sequential. Blocks can be nested to a maximum depth of 512 blocks. All statements except BEGIN and END are terminated by semicolons (;). No other character is valid for use as a terminator for PSQL statements.


In the Firebird 2.5 Language Reference, the declaration of local variables and cursors was considered part of the module header. With the introduction of UDR (external routines) in Firebird 3.0, we now consider this declaration section part of the — PSQL — module body. The External Module Body

The external module body specifies the UDR engine used to execute the external module, and optionally specifies the name of the UDR routine to call (<extname>) and/or a string (<extbody>) with UDR-specific semantics.

Configuration of external modules and UDR engines is not covered further in this Language Reference. Consult the documentation of a specific UDR engine for details.