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

This trigger should do what you asked.

   CREATE TRIGGER mytrigger BEFORE INSERT ON mytable
          IF new.group_id IS NULL
            SET new.group_id = new.id
          END IF
      END;

It's copied from a very similar example in the MYSQL documentation page.