有没有办法在不使用 cursor 的情况下循环遍历 TSQL 中的表变量？

Question

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

如果我想遍历行，那么声明和使用 cursor 是我唯一的选择吗？ 还有其他方法吗？

Answer 1

首先，你应该绝对确定你需要遍历每一行——基于集合的操作在我能想到的每一种情况下都会执行得更快，并且通常会使用更简单的代码。

根据您的数据，可能只使用SELECT语句进行循环，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

另一种选择是使用临时表：

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数量。

注意：如果您使用 SQL 服务器，您最好使用：

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（见下面约瑟夫的回答）。

Answer 2

快速说明一下，如果您使用的是 SQL 服务器（2008 及更高版本），则具有以下示例：

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

会更好地服务

While EXISTS(SELECT * From #Temp)

Count 必须触及表中的每一行， EXISTS只需要触及第一行。

Answer 3

这就是我的做法：

declare @RowNum int, @CustId nchar(5), @Name1 nchar(25)

select @CustId=MAX(USERID) FROM UserIDs     --start with the highest ID
Select @RowNum = Count(*) From UserIDs      --get total number of records
WHILE @RowNum > 0                          --loop until no more records
BEGIN   
    select @Name1 = username1 from UserIDs where USERID= @CustID    --get other info from that row
    print cast(@RowNum as char(12)) + ' ' + @CustId + ' ' + @Name1  --do whatever

    select top 1 @CustId=USERID from UserIDs where USERID < @CustID order by USERID desc--get the next one
    set @RowNum = @RowNum - 1                               --decrease count
END

没有游标，没有临时表，没有额外的列。 与大多数主键一样，USERID 列必须是唯一的 integer。

Answer 4

像这样定义您的临时表 -

declare @databases table
(
    RowID int not null identity(1,1) primary key,
    DatabaseID    int,
    Name        varchar(15),   
    Server      varchar(15)
)

-- insert a bunch rows into @databases

然后这样做 -

declare @i int
select @i = min(RowID) from @databases
declare @max int
select @max = max(RowID) from @databases

while @i <= @max begin
    select DatabaseID, Name, Server from @database where RowID = @i --do some stuff
    set @i = @i + 1
end

Answer 5

这是我的做法：

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] 因为我第一次阅读问题时可能跳过了“变量”这个词，所以这里有一个更新的回复......

---

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

Answer 6

如果您别无选择，只能逐行创建 FAST_FORWARD cursor。 它将与建立一个while循环一样快，并且更容易长期维护。

FAST_FORWARD 指定启用了性能优化的 FORWARD_ONLY、READ_ONLY cursor。 如果同时指定了 SCROLL 或 FOR_UPDATE，则无法指定 FAST_FORWARD。

Answer 7

另一种无需更改架构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

Answer 8

这将适用于 SQL SERVER 2012 版本。

declare @Rowcount int 
select @Rowcount=count(*) from AddressTable;

while( @Rowcount>0)
  begin 
 select @Rowcount=@Rowcount-1;
 SELECT * FROM AddressTable order by AddressId desc OFFSET @Rowcount ROWS FETCH NEXT 1 ROWS ONLY;
end 

Answer 9

您可以使用 while 循环：

While (Select Count(*) From #TempTable) > 0
Begin
    Insert Into @Databases...

    Delete From #TempTable Where x = x
End

Answer 10

轻量级，无需额外制作表格，如果您的桌子上有 integer ID

Declare @id int = 0, @anything nvarchar(max)
WHILE(1=1) BEGIN
  Select Top 1 @anything=[Anything],@id=@id+1 FROM Table WHERE ID>@id
  if(@@ROWCOUNT=0) break;

  --Process @anything

END

Answer 11

-- [PO_RollBackOnReject]  'FININV10532'
alter procedure PO_RollBackOnReject
@CaseID nvarchar(100)

AS
Begin
SELECT  *
INTO    #tmpTable
FROM   PO_InvoiceItems where CaseID = @CaseID

Declare @Id int
Declare @PO_No int
Declare @Current_Balance Money


While (Select ROW_NUMBER() OVER(ORDER BY PO_LineNo DESC) From #tmpTable) > 0
Begin
        Select Top 1 @Id = PO_LineNo, @Current_Balance = Current_Balance,
        @PO_No = PO_No
        From #Temp
        update PO_Details
        Set  Current_Balance = Current_Balance + @Current_Balance,
            Previous_App_Amount= Previous_App_Amount + @Current_Balance,
            Is_Processed = 0
        Where PO_LineNumber = @Id
        AND PO_No = @PO_No
        update PO_InvoiceItems
        Set IsVisible = 0,
        Is_Processed= 0
        ,Is_InProgress = 0 , 
        Is_Active = 0
        Where PO_LineNo = @Id
        AND PO_No = @PO_No
End
End

Answer 12

可以使用 cursor 来执行此操作：

创建 function [dbo].f_teste_loop 返回 @tabela 表 ( cod int, nome 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;

结尾

创建过程 [dbo].[sp_teste_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;

结尾

Answer 13

我真的不明白为什么您需要使用可怕cursor 。 但是，如果您使用的是 SQL 服务器版本 2005/2008，这是另一种选择
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

Answer 14

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，并且更容易编写和维护。

Answer 15

如果您有唯一的 ID，我更喜欢使用 Offset Fetch，您可以通过以下方式对表格进行排序：

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 window function。

Answer 16

Step1：在 select 语句下面为每条记录创建一个具有唯一行号的临时表。

select eno,ename,eaddress,mobno int,row_number() over(order by eno desc) as rno into #tmp_sri from emp 

Step2：声明需要的变量

DECLARE @ROWNUMBER INT
DECLARE @ename varchar(100)

Step3：从临时表中获取总行数

SELECT @ROWNUMBER = COUNT(*) FROM #tmp_sri
declare @rno int

Step4：根据在temp中创建的唯一行号循环临时表

while @rownumber>0
begin
  set @rno=@rownumber
  select @ename=ename from #tmp_sri where rno=@rno  **// You can take columns data from here as many as you want**
  set @rownumber=@rownumber-1
  print @ename **// instead of printing, you can write insert, update, delete statements**
end

Answer 17

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，但我没有看到使用 MIN 来获取你的下一个 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

Answer 18

这是我的解决方案，它使用了无限循环、 BREAK语句和@@ROWCOUNT function。 不需要游标或临时表，我只需要编写一个查询即可获取@databases表中的下一行：

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


-- Populate the [@databases] table with test data.
insert into @databases (DatabaseID, [Name], [Server])
select X.DatabaseID, X.[Name], X.[Server]
from (values 
    (1, 'Roger', 'ServerA'),
    (5, 'Suzy', 'ServerB'),
    (8675309, 'Jenny', 'TommyTutone')
) X (DatabaseID, [Name], [Server])


-- Create an infinite loop & ensure that a break condition is reached in the loop code.
declare @databaseId int;

while (1=1)
begin
    -- Get the next database ID.
    select top(1) @databaseId = DatabaseId 
    from @databases 
    where DatabaseId > isnull(@databaseId, 0);

    -- If no rows were found by the preceding SQL query, you're done; exit the WHILE loop.
    if (@@ROWCOUNT = 0) break;

    -- Otherwise, do whatever you need to do with the current [@databases] table row here.
    print 'Processing @databaseId #' + cast(@databaseId as varchar(50));
end

Answer 19

我同意上一篇文章，即基于集合的操作通常会执行得更好，但是如果您确实需要遍历这些行，我会采用以下方法：

1. 向表变量添加一个新字段（数据类型位，默认 0）
2. 插入您的数据
3. Select fUsed = 0的Top 1 Row （注意：fUsed是步骤1中的字段名称）
4. 执行您需要做的任何处理
5. 通过为记录设置 fUsed = 1 来更新表变量中的记录

6. Select 表中下一个未使用的记录并重复该过程

   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

Answer 20

这是我使用 2008 R2 的代码。 我正在使用的这段代码是在所有故事中的关键字段（SSNO 和 EMPR_NO）上建立索引

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 

Answer 21

SELECT @pk = @pk + 1

会更好：

SET @pk += @pk

如果您不引用表只是分配值，请避免使用 SELECT。