MySql difference between two timestamps in days?

If you’re happy to ignore the time portion in the columns, DATEDIFF() will give you the difference you’re looking for in days.

SELECT DATEDIFF('2010-10-08 18:23:13', '2010-09-21 21:40:36') AS days;
+------+
| days |
+------+
|   17 |
+------+