Elements Of PSQL

Elements of PSQL

A PSQL module may contain declarations of local variables, subroutines and cursors, assignments, conditional statements, loops, statements for raising custom exceptions, error handling and sending messages (events) to client applications.DML triggers have access to special context variables, two “records” that store, respectively, the NEW values for all columns during insert and update activity, and the OLD values during update and delete work, and three Boolean variables — INSERTING, UPDATING and DELETING — to determine the event that fired the trigger.

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

DML Statements with Parameters

If DML statements (SELECT, INSERT, UPDATE, DELETE, etc.) in the body of a 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.