Question

为什么会收到此错误

关键字
附近的语法不正确

当我执行以下代码时

SELECT *
FROM   [dbo].[priority_table] p
WHERE  EXISTS ( (SELECT 1
                 FROM   [dbo].[item_table] i
                 WHERE  i.priority_id = p.priority_id)
         AND filter = @filter )
        OR ( @filter IS NULL )

在过去的两个小时里，我的头部无法得到任何东西。当Where变量为@filter

时，我想忽略NULL子句

Answer 1

在Open parenthesis

之前移动EXISTS

SELECT *
FROM   [dbo].[priority_table] p
WHERE  ( EXISTS (SELECT 1
                 FROM   [dbo].[item_table] i
                 WHERE  i.priority_id = p.priority_id)
         AND filter = @filter )
        OR ( @filter IS NULL )

Answer 2

如果在[dbo]。[item_table]

中过滤列

SELECT *
FROM [dbo].[priority_table] p
WHERE EXISTS
            (SELECT 1
             FROM [dbo].[item_table] i
             WHERE (i.priority_id = p.priority_id
                   AND @filter = filter)
                  OR @filter IS NULL);

如果过滤器位于[dbo]。[priority_table]

SELECT *
FROM [dbo].[priority_table] p
WHERE(EXISTS
            (SELECT 1
             FROM [dbo].[item_table] i
             WHERE i.priority_id = p.priority_id)
      AND @filter = filter)
     OR @filter IS NULL;

Answer 3

这是无效的

EXISTS ( ( SELECT 1
             FROM   [dbo].[item_table] i
            WHERE  i.priority_id = p.priority_id 
         )
         AND filter = @filter 
       )

SELECT 1不等同于AND滤镜

Answer 4

这不是ju-ju魔术。 where子句中存在的内容就像子查询（特别是半连接）一样，因此（为了强调而添加额外的行）：

SELECT *
FROM   [dbo].[priority_table] p
WHERE  EXISTS 
(
    SELECT 1
    FROM   [dbo].[item_table] i
    WHERE  i.priority_id = p.priority_id
    AND (i.filter = @filter 
    OR  @filter IS NULL)
)

关键位是确保使用表别名，因此您可以正确引用子查询的外部和内部表。

Answer 5

或者更清楚地替代MotoGP的答案是（对@filter = 2没有任何假设）：

SELECT *
FROM   [dbo].[priority_table] p
WHERE  EXISTS 
(
    SELECT 1
    FROM   [dbo].[item_table] i
    WHERE  i.priority_id = p.priority_id
    AND i.filter = @filter
)
OR ( @filter IS NULL )

使用EXISTS时关键字附近的语法不正确

5 个答案: