SQL 子查询 NO 如果为空则执行答案

【问题标题】：SQL Sub Query NO execute if nullSQL 子查询 NO 如果为空则执行
【发布时间】：2009-07-23 16:52:11
【问题描述】：

我想知道如果我的@ID1 为NULL，是否有办法不执行我的子查询？

CREATE PROCEDURE [dbo].[TestTable_Search]
    @Col1 int,
    @Col2 uniqueidentifier,
    @Col3 datetime,
    @Col4 datetime,
    @ID1 varchar(10)
AS

SET TRANSACTION ISOLATION LEVEL READ COMMITTED

SELECT *

FROM
    [dbo].[TestTable]
WHERE
    [Col1] = COALESCE(@Col1, Col1) AND
    [Col2] = COALESCE(@Col2, Col2) AND
    [Col3] >= COALESCE(@Col3 + "00:00:00", Col3) AND
    [Col4] <= COALESCE(@Col4 + "23:59:59", Col4) AND
    [Col5] IN (SELECT [ID2] FROM [dbo].[TestTable2] WHERE [ID1] =  @ID1)

【问题讨论】：

标签： asp.net sql stored-procedures

【解决方案1】：

不确定你的意思，但也许这就是你要找的：

SELECT *
FROM
    [dbo].[TestTable]
WHERE
    [Col1] = COALESCE(@Col1, Col1) AND
    [Col2] = COALESCE(@Col2, Col2) AND
    [Col3] >= COALESCE(@Col3 + "00:00:00", Col3) AND
    [Col4] <= COALESCE(@Col4 + "23:59:59", Col4) AND (
    @ID1 IS NULL 
        OR [Col5] IN (SELECT [ID2] FROM [dbo].[TestTable2] WHERE [ID1] =  @ID1))

【讨论】：

优秀的正是我想要的...... +1

【解决方案2】：

SQL Server 在处理OR 条件方面不是很好，尤其是在变量方面，这就是为什么这可能是最好的决定：

SELECT  *
FROM    [dbo].[TestTable]
WHERE   [Col1] = COALESCE(@Col1, Col1) AND
        [Col2] = COALESCE(@Col2, Col2) AND
        [Col3] >= COALESCE(@Col3 + "00:00:00", Col3) AND
        [Col4] <= COALESCE(@Col4 + "23:59:59", Col4) AND
        AND @id1 IS NULL
UNION ALL
SELECT  *
FROM    [dbo].[TestTable]
WHERE   [Col1] = COALESCE(@Col1, Col1) AND
        [Col2] = COALESCE(@Col2, Col2) AND
        [Col3] >= COALESCE(@Col3 + "00:00:00", Col3) AND
        [Col4] <= COALESCE(@Col4 + "23:59:59", Col4) AND
        [Col5] IN (SELECT [ID2] FROM [dbo].[TestTable2] WHERE [ID1] =  @ID1)

如果@id 不是NULL，则第一个子查询将因为过滤器而不返回任何内容。

如果@id 是NULL，则第二个子查询将不返回任何内容，因为与NULL 的比较永远不会匹配，内部子查询将返回一个空集，并且col5 IN (SELECT …) 将永远不会满足。

SQL Server 可以在运行时有效地检测到这些东西，这就是为什么第二个子查询中的第一个几乎会立即被优化的原因。

OR 与 UNION ALL 的性能比较请参阅我的博客中的这篇文章：

IN with a comma separated list: SQL Server

【讨论】：

【解决方案3】：

如果您不执行子查询，则无论如何都不会返回任何行。因此，只需像这样使用单独的 SELECT 来处理这种情况：

IF @ID1 IS NULL
BEGIN

    SELECT *
    FROM dbo.[TestTable]
    WHERE 1 = 0

END
ELSE
BEGIN

    SELECT *

    FROM
        [dbo].[TestTable]
    WHERE
        [Col1] = COALESCE(@Col1, Col1) AND
        [Col2] = COALESCE(@Col2, Col2) AND
        [Col3] >= COALESCE(@Col3 + "00:00:00", Col3) AND
        [Col4] <= COALESCE(@Col4 + "23:59:59", Col4) AND
        [Col5] IN (SELECT [ID2] FROM [dbo].[TestTable2] WHERE [ID1] =  @ID1)

END

【讨论】：