MariaDB [test]> delimiter //

MariaDB [test]> create procedure prt(OUT a row type of mysql.user) begin select *

into a from mysql.user limit 1; end;//

Query OK, 0 rows affected (0.156 sec)

MariaDB [test]> create procedure use_prt() begin declare b row type of mysql.user; call prt(b); select b.user, b.host; end;//

Query OK, 0 rows affected (0.192 sec)

MariaDB [test]> call use_prt()//

+-------------+-----------+

| b.user      | b.host    |

+-------------+-----------+

| mariadb.sys | localhost |

+-------------+-----------+

1 row in set (0.012 sec)

Query OK, 1 row affected (0.012 sec)

MariaDB [test]> call prt(@a)//

ERROR 1241 (21000): Operand should contain 1 column(s)