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Databases
Postgresql trigger: last modified time
by: Scott Marlowe
|
April 2, 2003
Version: 1.0
Type: Sample Code (HOWTO)
Category: Databases
License: BSD License
Description: This is an unltra simple trigger written in plpgsql, the standard procedural language of postgresql. It updates the lm (last modified field) of a table every time a record is inserted or updated. Requires plpgsql.
-- FUNCTION --
CREATE FUNCTION modtime () RETURNS opaque AS '
BEGIN
new.lm :=''now'';
RETURN new;
END;
' LANGUAGE 'plpgsql';
-- TABLE --
CREATE TABLE dtest (
id int primary key,
fluff text,
lm timestamp without time zone
);
--TRIGGER --
CREATE TRIGGER dtest
BEFORE UPDATE or INSERT ON dtest FOR EACH ROW EXECUTE PROCEDURE
modtime(lm);
-- SQL TESTS --
INSERT INTO dtest (id, fluff) VALUES (1,'this is a test');
INSERT INTO dtest (id, fluff) VALUES (2,'this is another test');
SELECT * FROM dtest;
1 | this is a test | 2003-04-02 10:33:12.577089
2 | this is another test | 2003-04-02 10:33:18.591148
UPDATE dtest SET id=3 WHERE id=1;
3 | this is a test | 2003-04-02 10:34:52.219963 [1]
UPDATE dtest SET fluff='now is the time' WHERE id=2;
SELECT * FROM dtest WHERE id=2;
2 | now is the time | 2003-04-02 10:38:06.259443 [2]
UPDATE dtest SET lm='2003-04-02 08:30:00' WHERE id=3;
SELECT * FROM dtest WHERE id=3;
3 | this is a test | 2003-04-02 10:36:15.45687 [3]
[1] The timestamp has changed for this record when we changed the id field.
[2] The timestamp also changes for the fluff field.
[3] We tried to set lm, but the trigger on that field in dtest intercepted the change and forced it
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