MySQL(存储)过程 - 参数和查询

Question

我试图用参数创建一个简单的过程.

CALL new_procedure('mode', 'ASC');

第一个输入是列,第二个输入是排序方向

DELIMITER $$

CREATE DEFINER=`root`@`localhost` PROCEDURE `new_procedure`(IN in_order_by_column varchar(20), in_order_by_direction char(4))
BEGIN

    DECLARE order_by varchar(30);
    SET @order_by = CONCAT('`', in_order_by_column, '` ', in_order_by_direction);
/*
    SELECT * FROM `common_tags` ORDER BY @order_by  LIMIT 5;
*/
    SELECT @order_by as 'c';

END

在上面的例子中,我只输出了2个参数,这样我就可以看到发生了什么.

结果:

"c"
`mode` ASC

.

当我使用它的预期代码运行该程序时,如下所示.

DELIMITER $$

CREATE DEFINER=`root`@`localhost` PROCEDURE `new_procedure`(IN in_order_by_column varchar(20), in_order_by_direction char(4))
BEGIN

    DECLARE order_by varchar(30);
    SET @order_by = CONCAT('`', in_order_by_column, '` ', in_order_by_direction);
    SELECT * FROM `common_tags` ORDER BY @order_by  LIMIT 5;

END

结果

tags_id     data                mode        parent_id       position
1           Wood                2           13              6
2           Trippy              0           0               0
4           Artists             1           0               1
6           "Newest Additions"  1           0               11
12          "Natural Elements"  2           5               8

如您所见,结果未按类别排序mode.

任何帮助表示赞赏.

Answer 1

不幸的是,PREPARE在这种情况下你需要整个查询:

DELIMITER $$

DROP PROCEDURE IF EXISTS `new_procedure`$$

CREATE PROCEDURE `new_procedure`(IN in_order_by_column varchar(20), in_order_by_direction char(4))
BEGIN
    SET @buffer = CONCAT_WS('',
        'SELECT * FROM `common_tags` ORDER BY `', in_order_by_column, '` ', in_order_by_direction, ' LIMIT 5'
    );

    PREPARE stmt FROM @buffer;
    EXECUTE stmt;

    DEALLOCATE PREPARE stmt;
END$$

DELIMITER ;

注意:应该非常小心地使用所描述的方法,因为如果使用不正确,它对SQL注入攻击是难以理解的.