有没有办法在不使用游标的情况下在SQL中循环表变量？

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

如果我想迭代这些行，是声明和使用游标我唯一的选择吗？还有另一种方式吗？

Answer 1

首先，您应该绝对确定需要遍历每一行 - 基于集合的操作在我能想到的每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，可以使用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：如果您使用的是SQL Server，最好使用：

WHILE EXISTS(SELECT * FROM #Temp)

使用COUNT必须触及表格中的每一行，EXISTS只需要触及第一行（请参阅下面的Josef's answer）。

Answer 2

如果您使用的是SQL Server（2008及更高版本），请快速注意以下示例：

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

会更好

While EXISTS(SELECT * From #Temp)

Count必须触及表格中的每一行，EXISTS只需触摸第一行。

Answer 3

我就是这样做的：

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。 USERID列必须是唯一的整数，因为大多数主键都是。

Answer 4

像这样定义临时表 -

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

我将如何做到这一点：

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]因为我在第一次阅读问题时可能会跳过“变量”一词，这是一个更新的回复...

---

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，可以逐行创建FAST_FORWARD游标。它将与构建while循环一样快，并且在长期内更容易维护。

FAST_FORWARD     指定启用了性能优化的FORWARD_ONLY，READ_ONLY游标。如果还指定了SCROLL或FOR_UPDATE，则无法指定FAST_FORWARD。

Answer 7

另一种方法，无需更改架构或使用临时表：

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

-- [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 9

如果桌面上有一个整数file = io.open("output.txt","w") file:write("hello, reader!") file:close() ，则轻量级，无需制作额外的表格

ID

Answer 10

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 11

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)

这比任何循环技术快得多，并且更易于编写和维护。

Answer 12

我真的不明白为什么你需要使用可怕的cursor。 但是，如果您使用的是SQL Server 2005/2008版，则还有另一种选择
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

Answer 13

这将在SQL SERVER 2012版本中使用。

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 14

我同意之前的帖子，基于集合的操作通常会表现得更好，但是如果你确实需要迭代这些行，我会采取的方法：

1. 向表变量添加新字段（数据类型位，默认为0）
2. 插入数据
3. 选择fUsed = 0 的前1行（注意：fUsed是步骤1中字段的名称）
4. 执行您需要执行的任何处理
5. 通过为记录设置fUsed = 1来更新表变量中的记录

6. 从表格中选择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 15

此方法只需要一个变量，不会删除@databases中的任何行。我知道这里有很多答案，但是我没有看到一个使用MIN来获取你的下一个ID。

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 16

如果您有唯一ID，我更喜欢使用Offset Fetch，您可以按以下方式对表进行排序：

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

这样我就不需要在表中添加字段或使用窗口函数。

Answer 17

可以使用游标执行此操作：

创建函数[dbo] .f_teste_loop 返回@tabela表 （     cod int，     nome varchar（10） ） 如 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;

端

创建程序[dbo]。[sp_teste_loop] 如 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;

端

Answer 18

这是我的解决方案，它使用无限循环，BREAK语句和@@ROWCOUNT函数。不需要游标或临时表，我只需要编写一个查询来获取@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

这是我使用2008 R2的代码。我使用的这段代码是在关键字段（SSNO和EMPR_NO）上构建索引n所有故事

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 20

选择@pk = @pk + 1会更好：SET @pk + = @pk。如果你没有引用表，则避免使用SELECT只是分配值。

Answer 21

步骤1：在select语句下面创建一个临时表，每个记录都有唯一的行号。

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

步骤2：声明所需的变量

DECLARE @ROWNUMBER INT
DECLARE @ename varchar(100)

步骤3：从临时表中获取总行数

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

步骤4：基于在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