mysql> select 1 = '1a';
+----------+
| 1 = '1a' |
+----------+
|        1 |
+----------+
1 row in set, 1 warning (0.00 sec)

mysql> select 1 != '1a';
+-----------+
| 1 != '1a' |
+-----------+
|         0 |
+-----------+
1 row in set, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+---------+------+----------------------------------------+
| Level   | Code | Message                                |
+---------+------+----------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: '1a' |
+---------+------+----------------------------------------+