MySQL trigger to update a field to the value of id

Question

I would like to have a trigger to perform following operation for inserted records:

 # pseudocode
 if new.group_id is null
    set new.group_id = new.id
 els         


        

Answer 1

I believe that this will work for you

I have two tables

test_b: a_id, value
test_c: a_id, value

And here is a trigger on the insert of test b. It checks to see if a_id is null and if it is it inserts 0

CREATE TRIGGER test_b AFTER INSERT ON test_b
  FOR EACH ROW 
    INSERT INTO test_c (a_id, value) VALUES (IFNULL(NEW.a_id, 0),NEW.value)