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)
);

我的表将允许列（1-3）中的空值，但每个记录将基于这三个值是唯一的。然后我会有一个函数GetID(c1, c2, c3)，它将返回Id或无值

我知道我知道这不起作用：

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

那我怎么写这样的东西？

Answer 1

由于null与true运算符相比不会返回=，因此您必须使用IS NULL运算符明确检查它们：

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))

T-SQL查找记录并允许空值

1 个答案: