SQL子查詢不執行，如果爲空

Question

我想知道如果有一種方法不執行我的子查詢如果我的ID1爲NULL？

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) 

Answer 1

不知道你的意思，但也許這是你在找什麼：

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)) 

Answer 2

如果您不執行子查詢，則不會返回任何行。因此，只要處理這種情況下有獨立的選擇，像這樣：

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 

Answer 3

SQL Server不處理非常好OR條件，特別是變量，這就是爲什麼這可能將是最好的決定：

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NULL，由於過濾器，第一個子查詢將不返回任何內容。

如果@id是NULL，第二子查詢將返回任何結果，因爲相比於NULL永遠不匹配，內部子查詢將返回一個空集，col5 IN (SELECT …)將永遠不會滿足。

SQL Server可以在運行時高效地檢測這些事件，這就是爲什麼第一個第二個子查詢幾乎可以立即被優化。

請參閱本文中我的博客的OR性能比較反對UNION ALL：

• IN with a comma separated list: SQL Server