首先，你应该绝对确定你需要遍历每一行——基于行集的操作在我能想到的任何情况下都会执行得更快，通常会使用更简单的代码。

根据您的数据，可能只使用SELECT语句循环，如下所示:

Declare @Id int

While (Select Count(*) From ATable Where Processed = 0) > 0
Begin
    Select Top 1 @Id = Id From ATable Where Processed = 0

    --Do some processing here

    Update ATable Set Processed = 1 Where Id = @Id 

End

另一种方法是使用临时表:

Select *
Into   #Temp
From   ATable

Declare @Id int

While (Select Count(*) From #Temp) > 0
Begin

    Select Top 1 @Id = Id From #Temp

    --Do some processing here

    Delete #Temp Where Id = @Id

End

您应该选择的选项实际上取决于数据的结构和容量。

注意:如果您正在使用SQL Server，您将更好地使用:

WHILE EXISTS(SELECT * FROM #Temp)

使用COUNT将不得不触及表中的每一行，EXISTS只需要触及第一行(参见Josef的回答)。

我同意之前的帖子，基于集的操作通常会执行得更好，但如果你确实需要遍历行，下面是我将采取的方法:

Add a new field to your table variable (Data Type Bit, default 0) Insert your data Select the Top 1 Row where fUsed = 0 (Note: fUsed is the name of the field in step 1) Perform whatever processing you need to do Update the record in your table variable by setting fUsed = 1 for the record Select the next unused record from the table and repeat the process DECLARE @databases TABLE ( DatabaseID int, Name varchar(15), Server varchar(15), fUsed BIT DEFAULT 0 ) -- insert a bunch rows into @databases DECLARE @DBID INT SELECT TOP 1 @DBID = DatabaseID from @databases where fUsed = 0 WHILE @@ROWCOUNT <> 0 and @DBID IS NOT NULL BEGIN -- Perform your processing here --Update the record to "used" UPDATE @databases SET fUsed = 1 WHERE DatabaseID = @DBID --Get the next record SELECT TOP 1 @DBID = DatabaseID from @databases where fUsed = 0 END

以下是我的做法:

Select Identity(int, 1,1) AS PK, DatabaseID
Into   #T
From   @databases

Declare @maxPK int;Select @maxPK = MAX(PK) From #T
Declare @pk int;Set @pk = 1

While @pk <= @maxPK
Begin

    -- Get one record
    Select DatabaseID, Name, Server
    From @databases
    Where DatabaseID = (Select DatabaseID From #T Where PK = @pk)

    --Do some processing here
    -- 

    Select @pk = @pk + 1
End

[编辑]因为我可能在第一次读这个问题时跳过了“变量”这个词，这里是一个更新的回答…

declare @databases table
(
    PK            int IDENTITY(1,1), 
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)
-- insert a bunch rows into @databases
--/*
INSERT INTO @databases (DatabaseID, Name, Server) SELECT 1,'MainDB', 'MyServer'
INSERT INTO @databases (DatabaseID, Name, Server) SELECT 1,'MyDB',   'MyServer2'
--*/

Declare @maxPK int;Select @maxPK = MAX(PK) From @databases
Declare @pk int;Set @pk = 1

While @pk <= @maxPK
Begin

    /* Get one record (you can read the values into some variables) */
    Select DatabaseID, Name, Server
    From @databases
    Where PK = @pk

    /* Do some processing here */
    /* ... */ 

    Select @pk = @pk + 1
End

首先，你应该绝对确定你需要遍历每一行——基于行集的操作在我能想到的任何情况下都会执行得更快，通常会使用更简单的代码。

根据您的数据，可能只使用SELECT语句循环，如下所示:

Declare @Id int

While (Select Count(*) From ATable Where Processed = 0) > 0
Begin
    Select Top 1 @Id = Id From ATable Where Processed = 0

    --Do some processing here

    Update ATable Set Processed = 1 Where Id = @Id 

End

另一种方法是使用临时表:

Select *
Into   #Temp
From   ATable

Declare @Id int

While (Select Count(*) From #Temp) > 0
Begin

    Select Top 1 @Id = Id From #Temp

    --Do some processing here

    Delete #Temp Where Id = @Id

End

您应该选择的选项实际上取决于数据的结构和容量。

注意:如果您正在使用SQL Server，您将更好地使用:

WHILE EXISTS(SELECT * FROM #Temp)

使用COUNT将不得不触及表中的每一行，EXISTS只需要触及第一行(参见Josef的回答)。

这是我使用的2008 R2代码。我使用的这段代码是在所有故事的关键字段(SSNO & EMPR_NO)上构建索引

if object_ID('tempdb..#a')is not NULL drop table #a

select 'IF EXISTS (SELECT name FROM sysindexes WHERE name ='+CHAR(39)+''+'IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+char(39)+')' 
+' begin DROP INDEX [IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+'] ON '+table_schema+'.'+table_name+' END Create index IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+ ' on '+ table_schema+'.'+table_name+' ('+COLUMN_NAME+') '   'Field'
,ROW_NUMBER() over (order by table_NAMe) as  'ROWNMBR'
into #a
from INFORMATION_SCHEMA.COLUMNS
where (COLUMN_NAME like '%_SSNO_%' or COLUMN_NAME like'%_EMPR_NO_')
    and TABLE_SCHEMA='dbo'

declare @loopcntr int
declare @ROW int
declare @String nvarchar(1000)
set @loopcntr=(select count(*)  from #a)
set @ROW=1  

while (@ROW <= @loopcntr)
    begin
        select top 1 @String=a.Field 
        from #A a
        where a.ROWNMBR = @ROW
        execute sp_executesql @String
        set @ROW = @ROW + 1
    end 

我将提供基于集合的解决方案。

insert  @databases (DatabaseID, Name, Server)
select DatabaseID, Name, Server 
From ... (Use whatever query you would have used in the loop or cursor)

这比任何循环技术都要快得多，而且更容易编写和维护。