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

如果您别无选择,只能逐行创建FAST_FORWARD游标。它和构建while循环一样快,而且更容易长期维护。

FAST_FORWARD 指定一个启用性能优化的FORWARD_ONLY、READ_ONLY游标。如果还指定了SCROLL或FOR_UPDATE,则FAST_FORWARD不能指定。

其他回答

我真的不明白为什么你需要使用可怕的光标。 但是如果你使用的是2005/2008版本的SQL Server,还有另一种选择 使用递归

declare @databases table
(
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)

--; Insert records into @databases...

--; Recurse through @databases
;with DBs as (
    select * from @databases where DatabaseID = 1
    union all
    select A.* from @databases A 
        inner join DBs B on A.DatabaseID = B.DatabaseID + 1
)
select * from DBs

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

另一种不需要改变模式或使用临时表的方法:

DECLARE @rowCount int = 0
  ,@currentRow int = 1
  ,@databaseID int
  ,@name varchar(15)
  ,@server varchar(15);

SELECT @rowCount = COUNT(*)
FROM @databases;

WHILE (@currentRow <= @rowCount)
BEGIN
  SELECT TOP 1
     @databaseID = rt.[DatabaseID]
    ,@name = rt.[Name]
    ,@server = rt.[Server]
  FROM (
    SELECT ROW_NUMBER() OVER (
        ORDER BY t.[DatabaseID], t.[Name], t.[Server]
       ) AS [RowNumber]
      ,t.[DatabaseID]
      ,t.[Name]
      ,t.[Server]
    FROM @databases t
  ) rt
  WHERE rt.[RowNumber] = @currentRow;

  EXEC [your_stored_procedure] @databaseID, @name, @server;

  SET @currentRow = @currentRow + 1;
END

我更喜欢使用偏移获取,如果你有一个唯一的ID,你可以排序你的表:

DECLARE @TableVariable (ID int, Name varchar(50));
DECLARE @RecordCount int;
SELECT @RecordCount = COUNT(*) FROM @TableVariable;

WHILE @RecordCount > 0
BEGIN
SELECT ID, Name FROM @TableVariable ORDER BY ID OFFSET @RecordCount - 1 FETCH NEXT 1 ROW;
SET @RecordCount = @RecordCount - 1;
END

这样我就不需要向表中添加字段或使用窗口函数。

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