ERROR 1064 (42000) at line 39: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'isnull' at line 1

ERROR 1064 (42000) at line 39: You have an error in your SQL syntax;
check the manual that corresponds to your MySQL server version for the right syntax to use near ‘isnull’ at line 1 . How to solve this error?