Ok, in this question I learned how to prevent the insert of a NULL value. But, unfortunately, an empty string is being inserted anyway. Apart from preventing this on the PHP side, I'd like to use something like a database constraint to prevent this. Of course a check on the application side is necessary, but I'd like it to be on both sides.
I am taught that whatever application is talking to your database, it should not be able to insert basically wrong data in it. So...
CREATE TABLE IF NOT EXISTS tblFoo (
foo_id int(11) NOT NULL AUTO_INCREMENT,
foo_test varchar(50) NOT NULL,
PRIMARY KEY (foo_id)
INSERT INTO tblFoo (foo_test) VALUES ('');
Normally you would do that with CHECK constraint:
foo_test VARCHAR(50) NOT NULL CHECK (foo_test <> '')
Unfortunately MySQL has limited support for constraints. From MySQL Reference Manual:
The CHECK clause is parsed but ignored by all storage engines.
That's why you have to use triggers as a workaround, as people have pointed out.