Triggers, Rules, and Views - PostgreSQL Developer's Guide - page 82

To verify that the rows are inserted, use the following command:
warehouse_db=# SELECT warehouse_id, warehouse_name, state FROM
warehouse_tbl;
warehouse_id | warehouse_name | state
--------------+----------------+-------
1 | Mark Corp | CT
2 | Bill & Co | CT
(2 rows)
You can ind detailed references in the PostgreSQL manual, which is
available at http://www.postgresql.org/docs/9.4/static/
server-programming.html , about the PostgreSQL implementation
of triggers in native procedural languages with syntax and code.
We have already discussed that the trigger function gets input through a specially
passed TriggerData structure, which contains a set of local variables that we will use
in our trigger functions. This set of variables includes OLD , NEW , and other variables
that have TG_ at the start of their names, such as TG_WHEN , TG_TABLE_NAME .
Let's discuss these set of variables:
• NEW : This variable is of the RECORD type and contains the new row to be
stored for the INSERT / UPDATE command in row-level triggers
• OLD : This variable is also of the RECORD type and stores the old row for the
DELETE / UPDATE operation in row-level triggers
• TG_OP : This will contain one of the strings that informs you for which
operation the trigger is invoked; the value can be INSERT , UPDATE , DELETE , or
TRUNCATE
• TG_TABLE_NAME : This holds the name of the table for which the trigger is ired
• TG_WHEN : This will contain the string with the value of BEFORE , AFTER , or
INSTEAD OF , as per the trigger's deinition
After creating tables, deine a trigger function called warehouse_audit_func that
will log changes in the warehouse_audit table after an INSERT operation on the
warehouse_tbl table:
warehouse_db=# CREATE OR REPLACE FUNCTION warehouse_audit_func()
RETURNS trigger AS $first_trigger$
BEGIN
INSERT INTO warehouse_audit
(wlog_id, insertion_time)
VALUES