group_concat.sql

DELIMITER //
 
CREATE PROCEDURE grouping(IN _sql varchar(128), IN _col varchar(32))
BEGIN
    SET @sql = 
        CONCAT(
            CONCAT(
                CONCAT(
                    CONCAT(
                        'SELECT @in := GROUP_CONCAT(t.',
                        _col
                    ),
                    ' SEPARATOR \',\') FROM ('
                ),
                _sql
            ),
            ') as t;'
        );
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
END;
//
DELIMITER ;