Question

I have a trigger that sets a datetime field in a table row when a new row is inserted. (Don’t bother lecturing me that I could do this in the table definition, I have second datetime field that is using that functionality already and you can only do it with one column per table.)

This trigger works great for my purposes:

CREATE TRIGGER foobar_insert
    BEFORE INSERT ON foobar
        FOR EACH ROW SET NEW.created=NOW();

So whenever a new row is inserted, foobar.created gets set to the current time. This is great when I do something like:

INSERT INTO foobar (foo) VALUES (‘bar’);

The only problem with this is that if I want to explicitly set foobar.created in the insert statement, it gets overridden by the trigger.

So,

INSERT INTO foobar (foo,created) VALUES (‘foo’,’2006-01-01 12:12:12′);

results in foobar.created equaling the time of the insert, not the time specified in the insert statement.

So my question is: How can I change my trigger to only set foobar.created if it doesn’t already have a value?

EDIT:

In response to james_bond below, here is what worked:

DELIMITER $$
DROP TRIGGER IF EXISTS foobar_insert$$
CREATE TRIGGER foobar_insert
  BEFORE INSERT ON foobar
    FOR EACH ROW
      IF NEW.created IS NULL THEN
        SET NEW.created=NOW();
      END IF$$
DELIMITER ;

Note I had to include DELIMITER statements because the IF statement required an interior semicolon.

Answer 1

Test for NEW.created is NULL, if is set it’s because you have set it in your insert statement,if it is NULL then it needs the current time as value, something like this will do the trick:

if NEW.created is NULL THEN
   SET NEW.created = now();
end if