假设我有以下简单的表变量:

declare @databases table
(
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)
-- insert a bunch rows into @databases

如果我想遍历各行,声明和使用游标是我唯一的选择吗?还有别的办法吗?


当前回答

这种方法只需要一个变量,并且不会从@databases中删除任何行。我知道这里有很多答案,但我没有看到像这样使用MIN来获取下一个ID的答案。

DECLARE @databases TABLE
(
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)

-- insert a bunch rows into @databases

DECLARE @CurrID INT

SELECT @CurrID = MIN(DatabaseID)
FROM @databases

WHILE @CurrID IS NOT NULL
BEGIN

    -- Do stuff for @CurrID

    SELECT @CurrID = MIN(DatabaseID)
    FROM @databases
    WHERE DatabaseID > @CurrID

END

其他回答

可以使用游标来做到这一点:

创建函数[dbo].f_teste_loop 返回@tabela表 ( 鳕鱼int, 省varchar (10) ) 作为 开始

insert into @tabela values (1, 'verde');
insert into @tabela values (2, 'amarelo');
insert into @tabela values (3, 'azul');
insert into @tabela values (4, 'branco');

return;

end

创建过程[dbo].[sp_test_loop] 作为 开始

DECLARE @cod int, @nome varchar(10);

DECLARE curLoop CURSOR STATIC LOCAL 
FOR
SELECT  
    cod
   ,nome
FROM 
    dbo.f_teste_loop();

OPEN curLoop;

FETCH NEXT FROM curLoop
           INTO @cod, @nome;

WHILE (@@FETCH_STATUS = 0)
BEGIN
    PRINT @nome;

    FETCH NEXT FROM curLoop
           INTO @cod, @nome;
END

CLOSE curLoop;
DEALLOCATE curLoop;

end

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

简单说明一下,如果你使用的是SQL Server(2008及以上版本),下面的例子有:

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

会不会更好

While EXISTS(SELECT * From #Temp)

Count将不得不触及表中的每一行,EXISTS只需要触及第一行。

这种方法只需要一个变量,并且不会从@databases中删除任何行。我知道这里有很多答案,但我没有看到像这样使用MIN来获取下一个ID的答案。

DECLARE @databases TABLE
(
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)

-- insert a bunch rows into @databases

DECLARE @CurrID INT

SELECT @CurrID = MIN(DatabaseID)
FROM @databases

WHILE @CurrID IS NOT NULL
BEGIN

    -- Do stuff for @CurrID

    SELECT @CurrID = MIN(DatabaseID)
    FROM @databases
    WHERE DatabaseID > @CurrID

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。