mysql>
mysql> SELECT 'A\nB' REGEXP '^A$';
+---------------------+
| 'A\nB' REGEXP '^A$' |
+---------------------+
| 0 |
+---------------------+
1 row in set (0.00 sec)
mysql>
mysql> SELECT 'AA' REGEXP '^A';
+------------------+
| 'AA' REGEXP '^A' |
+------------------+
| 1 |
+------------------+
1 row in set (0.00 sec)
mysql>