mysql 增加字段前判斷是否存在

DELIMITER //
DROP PROCEDURE IF EXISTS schema_change;
CREATE PROCEDURE schema_change()
BEGIN
IF NOT EXISTS (SELECT * FROM information_schema.columns

WHERE table_schema = DATABASE()  AND table_name = 't_server' AND column_name = 'config') THEN

    ALTER TABLE t_server ADD COLUMN config  VARCHAR(255) ;
ELSE    
    ALTER TABLE t_server MODIFY COLUMN config VARCHAR(255) ;
END IF;
END //
DELIMITER ;

CALL schema_change();