仅当表中不存在记录时插入记录

您不必说什么版本的SQL Server。如果可以使用SQL Server 2008 MERGE

注意:通常将merge用于upsert,这是我最初认为的问题所在,但它在没有 WHEN MATCHED 条款和 WHEN NOT MATCHED 子句也适用于本例。示例用法。

CREATE TABLE #A(
 [id] [int] NOT NULL PRIMARY KEY CLUSTERED,
 [C] [varchar](200) NOT NULL)


    MERGE #A AS target
    USING (SELECT 3, 'C') AS source (id, C)
    ON (target.id = source.id)
    /*Uncomment for Upsert Semantics
       WHEN MATCHED THEN 
        UPDATE SET C = source.C */
    WHEN NOT MATCHED THEN    
        INSERT (id, C)
        VALUES (source.id, source.C);

在执行成本方面,当要执行插入操作时,这两个看起来大致相等…

Link to plan images for first run

但在第二次运行时,没有插入要做马修的答案看起来成本较低。我不确定是否有什么方法可以改善这一点。

Link to plan images for second run

测试脚本

select * 
into #testtable
from master.dbo.spt_values

CREATE UNIQUE CLUSTERED INDEX [ix] ON #testtable([type] ASC,[number] ASC,[name] ASC)


declare @name nvarchar(35)= 'zzz'
declare @number int = 50
declare @type nchar(3) = 'A'
declare @low int
declare @high int
declare @status int = 0;



MERGE #testtable AS target
USING (SELECT @name, @number, @type, @low, @high, @status) AS source (name, number, [type], low, high, [status])
ON (target.[type] = source.[type] AND target.[number] = source.[number] and target.[name] = source.[name] )
WHEN NOT MATCHED THEN    
INSERT (name, number, [type], low, high, [status])
VALUES (source.name, source.number, source.[type], source.low, source.high, source.[status]);

set @name = 'yyy'

IF NOT EXISTS 
    (SELECT *
    FROM #testtable
    WHERE [type] = @type AND [number] = @number and name = @name)
    BEGIN
INSERT INTO #testtable
(name, number, [type], low, high, [status])
VALUES (@name, @number, @type, @low, @high, @status);
END

IF NOT EXISTS 
    (SELECT {Columns} 
    FROM {Table} 
    WHERE {Column1 = SomeValue AND Column2 = SomeOtherVale AND ...}) 
INSERT INTO {Table} {Values}

简言之,您需要一个保证可以返回一行的表:

Insert dbo.Table (Col1, Col2, Col3....
Select 'Value1', 'Value2', 'Value3',....
From Information_Schema.Tables
Where Table_Schema = 'dbo'
    And Table_Name = 'Table'
    And Not Exists  (
                    Select 1
                    From dbo.Table
                    Where Col1 = 'Foo'
                        And Col2 = 'Bar'
                        And ....
                    )

我在野外也看到过这种变化:

Insert Table (Col1, Col2, Col3....
Select 'Value1', 'Value2', 'Value3'....
From    (
        Select 1 As Num
        ) As Z
Where Not Exists    (
                    Select 1
                    From Table
                    Where Col1 = Foo
                        And Col2 = Bar
                        And ....
                    ) 

我必须投赞成票 CONSTRAINT . 这是最简单、最有力的答案。我的意思是,看看其他答案有多复杂,我会说他们很难正确(并且保持正确)。

缺点是[1]从代码中不明显地看出,在数据库[2]中强制唯一性客户端代码必须知道才能捕获异常。换句话说,跟在你后面的人可能会想,“这是怎么工作的?”

撇开这一点:我曾经担心抛出/捕获异常会影响性能,但我做了一些测试(在SQL Server 2005上),结果并不重要。