Chapter 7: Procedural SQL (PSQL) Statements

Table of Contents

Elements of PSQL
Stored Procedures
Stored Functions
PSQL Blocks
Triggers
Writing the Body Code
Trapping and Handling Errors

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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 slight modifications to syntax in some cases.

Switching the Terminator in isql

Here we digress a little, to explain how to switch the terminator character in the isql utility to make it possible to define PSQL modules in that environment without conflicting with isql itself, which uses the same character, semicolon (;), as its own statement terminator.

isql Command SET TERM:

Used for: Changing the terminator character[s] to avoid conflict with the terminator character in PSQL statements

Available in: ISQL only

Syntax:

SET TERM <new_terminator> <old_terminator>

Table 7.1. SET TERM Parameters

Argument	Description
new_terminator	New terminator
old_terminator	Old terminator

When you write your triggers and stored procedures in isql, either in the interactive interface or in scripts, running a SET TERM statement is needed to switch the normal isql statement terminator from the semicolon to some other character or short string, to avoid conflict with the non-changeable semicolon terminator in PSQL. The switch to an alternative terminator needs to be done before you begin defining PSQL objects or running your scripts.

The alternative terminator can be any string of characters except for a space, an apostrophe or the current terminator character[s]. Any letter character[s] used will be case-sensitive.

Example: Changing the default semicolon to '^' (caret) and using it to submit a stored procedure definition: character as an alternative terminator character:

SET TERM ^;

CREATE OR ALTER PROCEDURE SHIP_ORDER (
    PO_NUM CHAR(8))
AS
BEGIN
  /* Stored procedure body */
END^

/* Other stored procedures and triggers */

SET TERM ;^

/* Other DDL statements */