Question

如果局部变量不为null，我想应用where子句。例如

declare @controlName nvarchar(250);

    SELECT 
        *
    FROM
    (
    SELECT  TOP (100) PERCENT 
        dbo.Blah.PageName, 
        dbo.BlahBlah.ControlName, 
        dbo.BlahBlah.ControlText, 
        'en' AS FriedEgg
    FROM         
        dbo.WebPageText INNER JOIN
        dbo.Blah ON dbo.BlahBlah.WebPageID = dbo.Blah.WebPageID

     if @controlName is not null

         WHERE dbo.BlahBlah.ControlName = IN(@controlName, not null)

因此，如果控件名称变量不为null，则应用where子句

Answer 1

最简单的答案......

SELECT TOP (100) PERCENT 
  dbo.Blah.PageName, 
  dbo.BlahBlah.ControlName, 
  dbo.BlahBlah.ControlText, 
  'en' AS FriedEgg
FROM         
  dbo.WebPageText
INNER JOIN
  dbo.Blah
    ON dbo.BlahBlah.WebPageID = dbo.Blah.WebPageID
WHERE
  dbo.BlahBlah.ControlName = @controlName
  OR @controlName IS NULL

Answer 2

如果这是针对SQL Server的，您可以尝试使用ISNULL函数：

DECLARE @controlName nvarchar(250);

SELECT 
    dbo.Blah.PageName, 
    dbo.BlahBlah.ControlName, 
    dbo.BlahBlah.ControlText, 
    'en' AS FriedEgg
FROM         
    dbo.WebPageText 
INNER JOIN
    dbo.Blah ON dbo.BlahBlah.WebPageID = dbo.Blah.WebPageID
WHERE 
    dbo.BlahBlah.ControlName = ISNULL(@controlName, dbo.BlahBlah.ControlName)

有了这个，如果@controlName是NOT NULL，那么您的WHERE子句就是：

WHERE 
    dbo.BlahBlah.ControlName = @controlName

但是如果@controlName 是 NULL，那么你得到

WHERE 
    dbo.BlahBlah.ControlName = dbo.BlahBlah.ControlName

并且总是如此，因此您不会限制结果集

Answer 3

...
WHERE dbo.BlahBlah.ControlName = COALESCE(@controlName, dbo.BlahBlah.ControlNmae)

Answer 4

尝试填充：

      WHERE @controlName is null OR rest_of_the_condition

如果@controlName为空，则无论WHERE如何，它都将评估为真，rest_of_the_condition子句为真。如果@controlName不为空，rest_of_the_condition子句中的WHERE将生效。

Answer 5

您是否尝试将IF测试放在WHERE子句中？

WHERE @controlName is not NULL AND dbo.BlahBlah.ControlName = IN(@controlName, not null)

Answer 6

可以使用T-SQL：

declare @controlName nvarchar(250);
IF(@controlName IS NULL)
BEGIN
    SELECT 
    *
    FROM
    (
    SELECT  TOP (100) PERCENT 
       dbo.Blah.PageName, 
       dbo.BlahBlah.ControlName, 
       dbo.BlahBlah.ControlText, 
       'en' AS FriedEgg
    FROM         
    dbo.WebPageText INNER JOIN
    dbo.Blah ON dbo.BlahBlah.WebPageID = dbo.Blah.WebPageID
END
ELSE
BEGIN
    SELECT 
    *
    FROM
    (
    SELECT  TOP (100) PERCENT 
        dbo.Blah.PageName, 
        dbo.BlahBlah.ControlName, 
        dbo.BlahBlah.ControlText, 
        'en' AS FriedEgg
    FROM         
    dbo.WebPageText INNER JOIN
    dbo.Blah ON dbo.BlahBlah.WebPageID = dbo.Blah.WebPageID
    WHERE dbo.BlahBlah.ControlName = @ControlName

END

如果符合条件，适用于条款

6 个答案: