在程序中指定了两次表，如何修复? [英] Table specified twice in Procedure, how to fix?

问题描述

我在尝试运行过程时收到此消息:

I got this message when attempted to run procedure:

程序是:

BEGIN

DECLARE v_user_id INT DEFAULT 0;
DECLARE v_order_id INT DEFAULT 0;
DECLARE v_min_price INT DEFAULT 0;

UPDATE `ordersperformers` SET `ordersperformers`.`Status` = 1

WHERE EXISTS (
SELECT 
@v_min_price = MIN(`ordersperformers`.`DeliveryPrice` + `ordersperformers`.`Price`), @v_user_id = `ordersperformers`.`Users_Id` = @v_user_id,
@v_order_id =`ordersperformers`.`Orders_Id`

    FROM `ordersperformers`

INNER JOIN
`orders` ON `orders`.`Id` = `ordersperformers`.`Orders_Id` WHERE
NOW() <= DATE_SUB(`orders`.`DeliveryDate`, INTERVAL 2 HOUR) AND `orders`.`Status` = 0 AND `ordersperformers`.`Status` = 0
) AND `ordersperformers`.`Orders_Id` = @v_order_id AND `ordersperformers`.`Users_Id` = @v_user_id;
END

如何解决?

推荐答案

我想你想要一个相关的子查询:

I think you want a correlated subquery:

UPDATE ordersperformers op
    SET op.Status = 1    
WHERE op.Status = 0 AND
      op.Orders_Id = @v_order_id AND
      op.Users_Id = @v_user_id AND
      EXISTS (SELECT  1
              FROM orders o
              WHERE o.id = op.Orders_Id AND
                    NOW() <= DATE_SUB(o.DeliveryDate, INTERVAL 2 HOUR) AND
                    o.Status = 0 
             );

我更改/修复了其他一些东西:

I changed/fixed a bunch of other things:

• 表别名使查询更易于编写和阅读.
• 反引号使查询更难编写和阅读.
• 仅在被更新的表上的条件应该在外部 WHERE 中，而不是在内部 WHERE 中.
• 在 EXISTS 子查询中设置变量根本没有意义.EXISTS 测试 行 是否存在.从逻辑上讲，它可以在不评估 SELECT 的情况下执行.

• Table aliases make the query easier to write and to read.
• Backticks make the query harder to write and read.
• Conditions only on the table being updated should be in the outer WHERE, not the inner WHERE.
• Setting variables in an EXISTS subquery simply does not make sense. EXISTS tests whether rows exist. Logically, it could execute without ever evaluating the SELECT.

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