CREATE SCHEMA IF NOT EXISTS common_schema;

DELIMITER $$

DROP FUNCTION IF EXISTS common_schema.add_ints $$

CREATE FUNCTION common_schema.add_ints(int_1 INT, int_2 INT) RETURNS INT NO SQL 

BEGIN 

    RETURN int_1 + int_2; 

END $$ 

DROP FUNCTION IF EXISTS common_schema.sum_ints $$

CREATE AGGREGATE FUNCTION common_schema.sum_ints(int_val INT) RETURNS INT 

BEGIN 

    DECLARE result INT DEFAULT 0; 

    DECLARE CONTINUE HANDLER FOR NOT FOUND RETURN result; 

    LOOP FETCH GROUP NEXT ROW; 

        SET result = common_schema.add_ints(result, int_val); 

    END LOOP; 

END $$

DELIMITER ;

MariaDB [test]> USE common_schema;

Database changed

MariaDB [common_schema]> SELECT common_schema.sum_ints(seq)

    -> FROM (SELECT 1 seq UNION ALL SELECT 2) t;

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

| common_schema.sum_ints(seq) |

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

|                           3 |

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

1 row in set (0.009 sec)

MariaDB [test]> USE another_schema;

Database changed

MariaDB [another_schema]> SELECT common_schema.sum_ints(seq) FROM (SELECT 1 seq UNION ALL SELECT 2) t;

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

| common_schema.sum_ints(seq) |

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

|                        NULL |

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

1 row in set (0.028 sec)