In a trigger how to insert values into another table but check if values already exists

Question

Based on my previous post found here im able to insert the values to the 2nd table when the status on first table changes, but it keeps adding indiscriminately, i need to check if the submit_id has already been inserted into the 2nd table and then update the fields not insert it gain, how would i do that check before the trigger is executed? Because the new.status and old.status refer to the row being edited not the row on table it's being inserted into, how can i compare that and insert or update if it already exists, Thanks

Answer 1

You can use INSERT INTO ... ON DUPLICATE KEY UPDATE syntax for that

If order for it to work properly you have to have a UNIQUE constraint on submitId column in your second table (let's call it students ).

ALTER TABLE students ADD UNIQUE (submitId);

Now an improved version of a trigger

DELIMITER $$
CREATE TRIGGER tg_au_submissions
AFTER UPDATE ON submissions
FOR EACH ROW
BEGIN
  IF NEW.status = 1 THEN
    INSERT INTO students (submitId, studentName, submitDate, contacts, email) 
    VALUES (NEW.submitId, NEW.studentName, NEW.submitDate, NEW.contacts, NEW.email)
    ON DUPLICATE KEY UPDATE 
      studentName = VALUES(studentName),
      submitDate = VALUES(submitDate),
      contacts = VALUES(contacts),
      email = VALUES(email);
  END IF;
END$$
DELIMITER ;

Here is SQLFiddle demo