SQL 服务器：更新 top(1) 循环

Question

我一直在查看其他条目，看起来我需要一个光标？我比较新，但我对这个很感兴趣。欢迎任何建议或帮助。

UPDATE top (1) dbo.table
SET [Status] = 1
WHERE [OrderId] = '1337' and [Status] = 0;
GO               

如果记录的 OrderID 为 1337，状态为 0，我希望将其更改为 1，但必须一次完成一个。

编辑：我想让它循环，直到没有 [Status] = 0

Answer 1

WHILE 1=1
    BEGIN
    UPDATE top (1) dbo.table
    SET [Status] = 1
    WHERE [OrderId] = '1337' and [Status] = 0

    IF @@ROWCOUNT = 0
        BREAK
    END

Answer 2

我也会把我的答案混在一起。我在需要小批量更新的生产系统中使用它。如果您想分批使用，可以将select top 100 PKid 更改为top 1。此方法允许您将更新的批次扩展到合理的范围，在最小锁定和基于集合的更新之间找到一个很好的折衷方案。显然，这比单个基于集合的语句增加了开销，但 OP 要求。

注意：我猜桌子上有一个 PK 字段，我只是给它起了一个假定名称 PKid

declare @done bit = 0x0;
declare @inputs table (PKid int primary key)

while @done = 0x0
begin
    -- clear the temp table variable
    delete from @inputs

    -- build the small batch up updates into table variable
    insert into @inputs (PKid) 
    select top 100 PKid from dbo.table where [Status] = 0 and OrderId = '1337'

    -- if we inserted zero records, set our @done bit to 'true' so the while loop breaks
    if @@rowcount = 0
    begin
        select @done = 0x1
    end

    -- make the update to the real table, constrained by the temp table variable
    update  t
    set     t.[Status] = 1
    from    dbo.table as t
    join    @inputs as i
    on      i.PKid = t.PKid
end

Answer 3

如果您只想用这句话更新一条记录，建议您执行以下操作：

UPDATE dbo.table
SET [Status] = 1
WHERE rowId in (Select top(1) rowId from dbo.Table where [OrderId] = '1337' and Status = 0);

我不知道您使用的是 Transact 还是 PL，因此您可能需要将 rowId 更改为 ROW_NUMBER。您也可以通过唯一标识符更改 rowId。 Where 子句将匹配“select”子句返回的唯一行。

您可以使用光标进行更新（与其他答案一样），但如果这是一次性的，这是一个快速的解决方案。

Answer 4

请避免使用 while 或光标循环来执行此操作。

这是一个更新“顶部”........解决方法：

http://granadacoder.wordpress.com/2009/07/06/update-top-n-order-by-example/

/* START TSQL */

    if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[Television]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
          BEGIN
                DROP TABLE [dbo].[Television]
          END
    GO


    CREATE TABLE [dbo].[Television] (
          TelevisionUUID [uniqueidentifier] not null default NEWSEQUENTIALID() , 
          TelevisionName varchar(64) not null , 
          TelevisionKey int not null , 
          IsCheckedOut bit default 0
    )     
    GO


    ALTER TABLE dbo.Television ADD CONSTRAINT PK_Television_TelevisionUUID
    PRIMARY KEY CLUSTERED (TelevisionUUID)
    GO


    ALTER TABLE dbo.Television ADD CONSTRAINT CK_Television_TelevisionName_UNIQUE 
    UNIQUE (TelevisionName)
    GO


    set nocount on

    declare @counter int
    select @counter = 11000
    declare @currentTVName varchar(24)
    declare @TopSize int
    select @TopSize = 10

    while @counter > 10000  /* this loop counter is ONLY here for fake data,….do not use this syntax for production code */
    begin

          select @currentTVName = 'TV:     '+ convert(varchar(24) , @counter)

          INSERT into dbo.Television ( TelevisionName , TelevisionKey ) values ( @currentTVName , @counter)

          select @counter = @counter - 1      
    end


    select count(*) as TV_Total_COUNT from dbo.Television 

    /*
    –Does not Work!
    Update TOP (10) dbo.Television
          Set IsCheckedOut = 1
    FROM
          dbo.Television tv
    ORDER BY tv.TelevisionKey
    */
    declare @AuditTrail table ( TelevisionUUID uniqueidentifier , OldIsCheckedOut bit , NewIsCheckedOut bit )

    ;
    WITH cte1 AS       
     (  SELECT 
          TOP (@TopSize) 

       TelevisionUUID , /* <<Note, the columns here must be available to the output */
       IsCheckedOut        
          FROM   
                dbo.Television tv      
        WITH ( UPDLOCK, READPAST , ROWLOCK ) /*  <<Optional Hints, but helps with concurrency issues   */
          WHERE  
                IsCheckedOut = 0              
          ORDER BY
                tv.TelevisionKey DESC        
    )
    UPDATE cte1
          SET  IsCheckedOut = 1
    output inserted.TelevisionUUID , deleted.IsCheckedOut , inserted.IsCheckedOut into @AuditTrail ( TelevisionUUID , OldIsCheckedOut , NewIsCheckedOut )
    ;
    print ''
    print 'Newly Checked Out Items'
    select * from dbo.Television tv where tv.IsCheckedOut <> 0

    print 'Output AuditTrail'
    select * from @AuditTrail
    print 'Not checked out items'
    select count(*) as TVCOUNTIsNOTCheckedOut from dbo.Television tv where tv.IsCheckedOut = 0