mySQL UPDATE query returns “0 rows affected”

Question

I have this query:

UPDATE phonecalls 
   SET Called = \"Yes\" 
 WHERE PhoneNumber = \"999 29-4655\"

My table is phonecalls, I

Answer 1

For the benefit of anyone here from Google, this problem was caused by me because I was trying to append to an empty field using CONCAT().

UPDATE example SET data=CONCAT(data, 'more');

If data is NULL, then CONCAT() returns NULL (ignoring the second parameter), so the value does not change (updating a NULL value to be a NULL value), hence the 0 rows updated.

In this case changing to the CONCAT_WS() function instead fixed the problem.