mysql> select * from test1;
    +---+------+
    | a | b    |
    +---+------+
    | 5 |    6 |
    | 3 |    4 |
    | 1 |    2 |
    +---+------+
    3 rows in set (0.03 sec)

    mysql> prepare ff from "select * from test1 where a=?";
    Query OK, 0 rows affected (0.00 sec)
    Statement prepared

    mysql> set @aa=3;
    Query OK, 0 rows affected (0.00 sec)

    mysql> execute ff using @aa;
    +---+------+
    | a | b    |
    +---+------+
    | 3 |    4 |
    +---+------+
    1 row in set (0.06 sec)