[英]SQL Server If condition at where clause?
我想进行选择查询,我有几个参数,但是根据值,我将参数添加到where子句中。 我不想使用动态查询。 例如,这是我存储的声明:
EXEC GETProducts @ProductID INT = -1, @ProductName NVARCHAR(100) = NULL, @ProductManufacturerID INT = -1
我想要由ManufacturerID = 3制造的所有产品
EXEC GETProducts -1, NULL, 3
我想要这样的查询,我知道它没有用,我也用CASE尝试过,但是没有用。
SELECT * FROM Product
WHERE
IF(@ProductID > -1)
BEGIN
ProductID = @ProductID
END
AND
IF(@ProductName <> '')
BEGIN
ProductName = @ProductName
END
AND
IF(@ProductManufacturerID > -1)
BEGIN
ProductManufacturerID = @ProductManufacturerID
END
谢谢你的帮助!!!
听起来您想要AND
与OR
的组合,而不是CASE
或IF
:
SELECT * FROM Product
WHERE
(@ProductID <= -1 OR ProductID = @ProductID)
AND
(@ProductName = '' OR ProductName = @ProductName)
AND
(@ProductManufacturerID <= -1 OR ProductManufacturerID = @ProductManufacturerID)
但是我会注意到,在特殊情况下, NULL
通常比“魔术”数字和字符串更可取:
SELECT * FROM Product
WHERE
(@ProductID IS NULL OR ProductID = @ProductID)
AND
(@ProductName IS NULL OR ProductName = @ProductName)
AND
(@ProductManufacturerID IS NULL OR ProductManufacturerID = @ProductManufacturerID)
SELECT *
FROM Product
WHERE
(@ProductID = -1 OR ProductID = @ProductID)
AND (@ProductName = '' OR ProductName = @ProductName)
AND (@ProductManufacturerID = -1 OR ProductManufacturerID = @ProductManufacturerID)
我想在这里。 您可能想写:
WHERE
(@ProductID > -1 AND ProductID = @ProductID)
OR
(@ProductName <> '' AND ProductName = @ProductName )
OR
(@ProductManufacturerID > -1 AND ProductManufacturerID = @ProductManufacturerID)
您可以通过将它们与OR
子句配对来创建“条件” WHERE
子句。 像这样:
SELECT * FROM Product
WHERE
(@ProductID <= -1 OR ProductID = @ProductID)
AND @ProductName = '' OR ProductName = @ProductName)
-- etc.
这样,如果“条件检查”为true,则不会评估OR
子句的后半部分。
通过将条件设为复合条件,您可以将查询更改为如下所示,并且不需要CASE
表达式。 顺便说一句, IF .. ELSE
构造仅在程序主体内起作用。
SELECT * FROM Product
WHERE (@ProductID > -1 AND ProductID = @ProductID)
AND (@ProductName <> '' AND ProductName = @ProductName)
AND (@ProductManufacturerID > -1 AND ProductManufacturerID = @ProductManufacturerID)
您可以在WHERE子句中将条件转换为需求。
IF(@ProductID > -1)
BEGIN
ProductID = @ProductID
END
等效于:
ProductID > -1 AND ProductID = @ProductID
,
IF(@ProductName <> '')
BEGIN
ProductName = @ProductName
END
等效于:
ProductName <> '' AND ProductName = @ProductName
,
IF(@ProductManufacturerID > -1)
BEGIN
ProductManufacturerID = @ProductManufacturerID
END
等效于:
ProductManufacturerID > -1 AND ProductManufacturerID = @ProductManufacturerID
因此,您的最终查询将是:
SELECT * FROM Product WHERE
ProductID > -1 AND
ProductID = @ProductID AND
ProductName <> '' AND
ProductName = @ProductName AND
ProductManufacturerID > -1 AND
ProductManufacturerID = @ProductManufacturerID
当您的参数打算影响选择查询时,案例将评估为1,因此使其成为select语句的一部分;否则,它将为0,因此将不计数,因为0 = 1将评估为false。
SELECT * FROM Product
WHERE
(CASE
WHEN @ProductId > -1 AND ProductId = @ProductId THEN 1
ELSE 0
END) = 1
AND
(CASE
WHEN @ProductName <> '' AND ProductName = @ProductName THEN 1
ELSE 0
END) = 1
AND
(CASE
WHEN @ProductManufacturerID > -1 AND ProductManufacturerID = @ProductManufacturerID THEN 1
END);
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