how to check if a table row exist with a trigger?

Question

i want to check if a table row exist with a trigger. if it does then it does nothing, but if it doesnt exist it inserts a row.

here is my current code i want to modify.

BEGIN
IF (NEW.counter >= 100) THEN
// check if a certain row exists in another table, if not, execute the beneath code
INSERT INTO tagCategories (name, counter) VALUES ('unnamed', NEW.counter);
UPDATE tagCategories2tagPairs SET tagCategoryId = LAST_INSERT_ID() WHERE tagPairId = OLD.id;
END IF;
END

is there any good tutorials on this, teaching all functions you can use with a trigger (they dont look like the php functions)

Answer 1

mysql trigger tutorial

CREATE TRIGGER Syntax

For the restrictions on behaviour allowed in Triggers, please see:

D.1. Restrictions on Stored Routines, Triggers, and Events

To check if row exists and update it, otherwise insert a row if it does not exist, you can use the INSERT INTO ... ON DUPLICATE KEY UPDATE statement, but within the restrictions for triggers mentioned in the above link.