T-SQL查找記錄並允許爲空

Question

CREATE TABLE [dbo].[Table1] (
    [Id]  INT   IDENTITY (1, 1) NOT NULL, 
    [Column1] VARCHAR (3) NULL, 
    [Column2] VARCHAR (2) NULL, 
    [Column3] VARCHAR (255) NULL, 
    PRIMARY KEY CLUSTERED ([Id] ASC), 
    CONSTRAINT [TableCon] UNIQUE NONCLUSTERED ([Column1] ASC, [Column2] ASC, [Column3] ASC) 
); 

我的表允許在列（1-3）中使用空值，但每個記錄基於這三個值將是唯一的。然後，我將有一個功能GetID(c1, c2, c3)這將返回所述1D或沒有價值

我知道，我知道，這是不行的：

SELECT Id 
FROM Table1 
WHERE Column1 = @c1 
AND Column2 = @c2 
AND Column3 = @c3 

因此，如何將我寫這樣的事情？

Answer 1

由於null當與=運營商相比，不返回true，你必須與IS NULL運營商明確地查詢到：

SELECT Id 
FROM Table1 
WHERE ((Column1 = @c1) OR (Column1 IS NULL AND @c1 IS NULL)) AND 
     ((Column2 = @c2) OR (Column2 IS NULL AND @c2 IS NULL)) AND 
     ((Column3 = @c3) OR (Column3 IS NULL AND @c3 IS NULL))