Match either zero or one a character: a? : Zero or One « Regular Expressions « MySQL Tutorial

1. MySQL Tutorial
2. Regular Expressions
3. Zero or One

mysql>
mysql> SELECT 'ABC' REGEXP '^Aa?C';
+----------------------+
| 'ABC' REGEXP '^Aa?C' |
+----------------------+
|                    0 |
+----------------------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT 'ABC' REGEXP '^ABa?C';
+-----------------------+
| 'ABC' REGEXP '^ABa?C' |
+-----------------------+
|                     1 |
+-----------------------+
1 row in set (0.00 sec)

mysql>
mysql> SELECT 'ABC' REGEXP '^Ba?C';
+----------------------+
| 'ABC' REGEXP '^Ba?C' |
+----------------------+
|                    0 |
+----------------------+
1 row in set (0.00 sec)

mysql>