mysql>
mysql> SELECT '1+2' REGEXP '1+2';
+--------------------+
| '1+2' REGEXP '1+2' |
+--------------------+
| 0 |
+--------------------+
1 row in set (0.00 sec)
mysql> SELECT '1+2' REGEXP '1\+2';
+---------------------+
| '1+2' REGEXP '1\+2' |
+---------------------+
| 0 |
+---------------------+
1 row in set (0.00 sec)
mysql> SELECT '1+2' REGEXP '1\\+2';
+----------------------+
| '1+2' REGEXP '1\\+2' |
+----------------------+
| 1 |
+----------------------+
1 row in set (0.00 sec)
mysql>