mysql: процедуры и функции

mysql> select * from user;
+----+-------+
| id | uname |
+----+-------+
|  1 | vasya |
|  2 | vova  |
+----+-------+
2 rows in set (0.00 sec)

mysql> select * from pay;
+----+------+------+
| id | usid | pay  |
+----+------+------+
|  1 | 1    |   10 |
|  2 | 1    |   10 |
|  3 | 1    |   10 |
|  4 | 1    |   15 |
+----+------+------+
4 rows in set (0.00 sec)

mysql> select * from balance;
+----+------+------+
| id | usid | val  |
+----+------+------+
|  1 |    1 |    9 |
|  2 |    1 |    7 |
|  3 |    1 |   11 |
|  4 |    1 |   23 |
|  5 |    1 |    3 |
+----+------+------+
5 rows in set (0.01 sec)

mysql> select sum(pay) from pay where usid=1 into @a;
Query OK, 1 row affected (0.00 sec)

mysql> select sum(val) from balance where usid=1 into @b;
Query OK, 1 row affected (0.00 sec)

mysql> select if (@a>@b,1,0);
+----------------+
| if (@a>@b,1,0) |
+----------------+
|              0 |
+----------------+
1 row in set (0.00 sec)

mysql> select if (@a>@b,1,0),@a,@b;
+----------------+------+------+
| if (@a>@b,1,0) | @a   | @b   |
+----------------+------+------+
|              0 | 45   | 53   |
+----------------+------+------+
1 row in set (0.01 sec)

select check_user('vasya');