SQL Server上INSERT或UPDATE的解决方案

现在它真的只是一个IO操作,但可怕的代码:-(

不要忘记交易.性能很好,但简单(IF EXISTS ..)方法非常危险.
当多个线程尝试执行插入或更新时,您可以轻松地获得主键冲突.

@Beau Crawford和@Esteban提供的解决方案显示了一般性的想法,但容易出错.

为了避免死锁和PK违规,您可以使用以下内容:

begin tran
if exists (select * from table with (updlock,serializable) where key = @key)
begin
   update table set ...
   where key = @key
end
else
begin
   insert into table (key, ...)
   values (@key, ...)
end
commit tran

要么

begin tran
   update table with (serializable) set ...
   where key = @key

   if @@rowcount = 0
   begin
      insert into table (key, ...) values (@key,..)
   end
commit tran

做一个UPSERT:

UPDATE MyTable SET FieldA=@FieldA WHERE Key=@Key

IF @@ROWCOUNT = 0
   INSERT INTO MyTable (FieldA) VALUES (@FieldA)

http://en.wikipedia.org/wiki/Upsert

很多人会建议你使用MERGE,但我提醒你不要这样做.默认情况下,它不会保护您不受多个语句的并发和竞争条件的影响,但它确实会引入其他危险:

http://www.mssqltips.com/sqlservertip/3074/use-caution-with-sql-servers-merge-statement/

即使使用这种"更简单"的语法,我仍然更喜欢这种方法(为简洁省略了错误处理):

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
BEGIN TRANSACTION;
UPDATE dbo.table SET ... WHERE PK = @PK;
IF @@ROWCOUNT = 0
BEGIN
  INSERT dbo.table(PK, ...) SELECT @PK, ...;
END
COMMIT TRANSACTION;

很多人会这样建议:

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
BEGIN TRANSACTION;
IF EXISTS (SELECT 1 FROM dbo.table WHERE PK = @PK)
BEGIN
  UPDATE ...
END
ELSE
  INSERT ...
END
COMMIT TRANSACTION;

但所有这一切都可以确保您可能需要两次读取表以找到要更新的行.在第一个示例中,您只需要找到一次行.(在这两种情况下,如果从初始读取中找不到行,则会发生插入.)

其他人会建议这样:

BEGIN TRY
  INSERT ...
END TRY
BEGIN CATCH
  IF ERROR_NUMBER() = 2627
    UPDATE ...
END CATCH

但是,如果除了在几乎每个插入失败的罕见情况下,除了让SQL Server捕获您可能首先阻止的异常之外没有其他原因,这是有问题的.我在这里证明了这一点:

http://www.mssqltips.com/sqlservertip/2632/checking-for-potential-constraint-violations-before-entering-sql-server-try-and-catch-logic/

http://www.sqlperformance.com/2012/08/t-sql-queries/error-handling

IF EXISTS (SELECT * FROM [Table] WHERE ID = rowID)
UPDATE [Table] SET propertyOne = propOne, property2 . . .
ELSE
INSERT INTO [Table] (propOne, propTwo . . .)

编辑:

唉,即使对我自己有害,我必须承认,没有选择的解决方案似乎更好,因为他们只需少一步即可完成任务.

如果要一次UPSERT多个记录,可以使用ANSI SQL:2003 DML语句MERGE.

MERGE INTO table_name WITH (HOLDLOCK) USING table_name ON (condition)
WHEN MATCHED THEN UPDATE SET column1 = value1 [, column2 = value2 ...]
WHEN NOT MATCHED THEN INSERT (column1 [, column2 ...]) VALUES (value1 [, value2 ...])

在SQL Server 2005中查看模仿MERGE语句.

虽然对此发表评论已经很晚了,但我想用MERGE添加一个更完整的例子.

此类Insert + Update语句通常称为"Upsert"语句,可以使用SQL Server中的MERGE实现.

这里给出了一个很好的例子:http: //weblogs.sqlteam.com/dang/archive/2009/01/31/UPSERT-Race-Condition-With-MERGE.aspx

以上解释了锁定和并发方案.

我将引用相同的参考:

ALTER PROCEDURE dbo.Merge_Foo2
      @ID int
AS

SET NOCOUNT, XACT_ABORT ON;

MERGE dbo.Foo2 WITH (HOLDLOCK) AS f
USING (SELECT @ID AS ID) AS new_foo
      ON f.ID = new_foo.ID
WHEN MATCHED THEN
    UPDATE
            SET f.UpdateSpid = @@SPID,
            UpdateTime = SYSDATETIME()
WHEN NOT MATCHED THEN
    INSERT
      (
            ID,
            InsertSpid,
            InsertTime
      )
    VALUES
      (
            new_foo.ID,
            @@SPID,
            SYSDATETIME()
      );

RETURN @@ERROR;

/*
CREATE TABLE ApplicationsDesSocietes (
   id                   INT IDENTITY(0,1)    NOT NULL,
   applicationId        INT                  NOT NULL,
   societeId            INT                  NOT NULL,
   suppression          BIT                  NULL,
   CONSTRAINT PK_APPLICATIONSDESSOCIETES PRIMARY KEY (id)
)
GO
--*/

DECLARE @applicationId INT = 81, @societeId INT = 43, @suppression BIT = 0

MERGE dbo.ApplicationsDesSocietes WITH (HOLDLOCK) AS target
--set the SOURCE table one row
USING (VALUES (@applicationId, @societeId, @suppression))
    AS source (applicationId, societeId, suppression)
    --here goes the ON join condition
    ON target.applicationId = source.applicationId and target.societeId = source.societeId
WHEN MATCHED THEN
    UPDATE
    --place your list of SET here
    SET target.suppression = source.suppression
WHEN NOT MATCHED THEN
    --insert a new line with the SOURCE table one row
    INSERT (applicationId, societeId, suppression)
    VALUES (source.applicationId, source.societeId, source.suppression);
GO

根据您的需要替换表和字段名称.注意使用ON条件.然后在DECLARE行上为变量设置适当的值(和类型).

干杯.

您可以使用MERGEStatement,此语句用于插入数据(如果不存在)或更新(如果存在).

MERGE INTO Employee AS e
using EmployeeUpdate AS eu
ON e.EmployeeID = eu.EmployeeID`

如果要先执行UPDATE if-no-rows-updated然后执行INSERT路由，请考虑先执行INSERT以防止出现争用情况（假设中间没有DELETE）

INSERT INTO MyTable (Key, FieldA)
   SELECT @Key, @FieldA
   WHERE NOT EXISTS
   (
       SELECT *
       FROM  MyTable
       WHERE Key = @Key
   )
IF @@ROWCOUNT = 0
BEGIN
   UPDATE MyTable
   SET FieldA=@FieldA
   WHERE Key=@Key
   IF @@ROWCOUNT = 0
   ... record was deleted, consider looping to re-run the INSERT, or RAISERROR ...
END

除了避免出现竞争状况外，如果在大多数情况下该记录将已经存在，那么这将导致INSERT失败，从而浪费CPU。

从SQL2008起，最好使用MERGE。