User Comments

A DROP TRIGGER fails if the table doesn't exists, so drop tiggers before.

DROP TRIGGER cannot be used together with the handy MYSQL extension "IF EXISTS". Other 5.0 features, like PROCEDUREs and FUNCTIONs however, do have this feature.

If you want to test for the existence of a trigger before removing it, you can do the following test before you delete it:

SELECT COUNT(*) FROM information_schema.TRIGGERS where TRIGGER_NAME = {yourtriggerhere};

We really need the "IF EXISTS" functionality. However, we are currently using 5.0.22. So, I came up with the example below. It is a bit complicated because of the lack of anonymous block support.

DROP TABLE IF EXISTS foo;

CREATE TABLE foo(i INTEGER);

DROP PROCEDURE IF EXISTS foo_trigger_deleter;

DELIMITER //

CREATE PROCEDURE foo_trigger_deleter
()
BEGIN
DECLARE l_count INTEGER;

SELECT count(*)
INTO l_count
FROM information_schema.TRIGGERS
WHERE TRIGGER_NAME = 'foo_trigger_deleter';

IF (l_count > 0)
THEN
DROP TRIGGER foo_trigger_deleter;
END IF;
END//

DELIMITER ;

call foo_trigger_deleter();

DROP PROCEDURE foo_trigger_deleter;

CREATE TRIGGER foo_trigger
BEFORE INSERT ON foo
FOR EACH ROW
SET NEW.i = NEW.i + 1;

@Kevin Regan

Supposing one can have several similar schemata (like dev, test, etc.), I think it's better to include the schema in the where clause of the select checking trigger existence:
SELECT count(*)
INTO l_count
FROM information_schema.TRIGGERS
WHERE TRIGGER_NAME = '<trigger_name>'
AND TRIGGER_SCHEMA = SCHEMA();

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