I am trying to write a trigger which can fill a table say A before inserting data in B.

There are atleast 3 tables which i have to deal with before i can insert data in A.

First i have to get an id from B then compare it with table C and get a field from there once i get the field i have to get id from A based on the values from C.

I have written a trigger which shows errors. I have gone through some sites but failed in gaining relevent information.

Can anyont suggest if its good to write such a trigger or is it better to do it programmatically in php.

Heres my trigger..

DROP TRIGGER IF EXISTS `forum_course_create`;
DELIMITER //
CREATE TRIGGER `forum_course_create` BEFORE INSERT ON `course`
FOR EACH ROW BEGIN
DECLARE x VARCHAR(50);
SET x = (select cat_name from category where cat_id = NEW.cat_id);
DECLARE y INTEGER
SET y = (select id from forum_category where category_name = x);
insert into forum_category (category_name,category_desc,parent_category) values (NEW.course_name,NEW.course_description,y);
END IF
END
//
DELIMITER ;

Keep all the DECLARE statements as the first statements in your code:

Also what happens if the SELECT statements do not return any value. You should include some kind of handler in there

DECLARE CONTINUE HANDLER FOR NOT FOUND SET ....