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mysql> \d $$mysql> DROP PROCEDURE IF EXISTS p5 $$Query OK, 0 rows affected, 1 warning (0.00 sec)mysql> CREATE PROCEDURE p5 (IN v_in INT, INOUT v_io INT, OUT v_out INT)    ->   BEGIN    ->     SELECT v_in, v_io, v_out;    ->     SET v_in = 10;    ->     SET v_io = 10;    ->     SET v_out = 10;    ->     SELECT v_in, v_io, v_out;    ->   END;    -> $$Query OK, 0 rows affected (0.00 sec)mysql> \d ;mysql> SET @a = 5; SET @b = 5; SET @c = 5;Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)Query OK, 0 rows affected (0.00 sec)mysql> CALL p5(@a, @b, @c);+------+------+-------+| v_in | v_io | v_out |+------+------+-------+|    5 |    5 |  NULL | +------+------+-------+1 row in set (0.00 sec)+------+------+-------+| v_in | v_io | v_out |+------+------+-------+|   10 |   10 |    10 | +------+------+-------+1 row in set (0.00 sec)Query OK, 0 rows affected (0.00 sec)mysql> SELECT @a, @b, @c;+------+------+------+| @a   | @b   | @c   |+------+------+------+| 5    | 10   | 10   | +------+------+------+1 row in set (0.00 sec)