CODEWITHSUNDEEP
sql-servert-sqlloops
Ray
Ray

Reputation: 192186

Is there a way to loop through a table variable in TSQL without using a cursor?

Let's say I have the following simple table variable:

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

Is declaring and using a cursor my only option if I wanted to iterate through the rows? Is there another way?

Upvotes: 311

Views: 847439

Answers (21)

Martynnw
Martynnw

Reputation: 10895

First of all you should be absolutely sure you need to iterate through each row — set based operations will perform faster in every case I can think of and will normally use simpler code.

Depending on your data it may be possible to loop using just SELECT statements as shown below:

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

Another alternative is to use a temporary table: 

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

The option you should choose really depends on the structure and volume of your data.

Note: If you are using SQL Server you would be better served using:

WHILE EXISTS(SELECT * FROM #Temp)

Using COUNT will have to touch every single row in the table, the EXISTS only needs to touch the first one (see Josef's answer below).

Upvotes: 457

Bob Alley
Bob Alley

Reputation: 1

SELECT @pk = @pk + 1

would be better: 

SET @pk += @pk

Avoid using SELECT if you are not referencing tables are are just assigning values.

Upvotes: 0

Josef
Josef

Reputation: 7609

Just a quick note, if you are using SQL Server (2008 and above), the examples that have:

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

Would be better served with 

While EXISTS(SELECT * From #Temp)

The Count will have to touch every single row in the table, the EXISTS only needs to touch the first one.

Upvotes: 156

Mass Dot Net
Mass Dot Net

Reputation: 2259

Here's my solution, which makes use of an infinite loop, the BREAK statement, and the @@ROWCOUNT function. No cursors or temporary table are necessary, and I only need to write one query to get the next row in the @databases table:

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

Upvotes: 1

Alexandre Pezzutto
Alexandre Pezzutto

Reputation: 31

It's possible to use a cursor to do this:

create function [dbo].f_teste_loop returns @tabela table ( cod int, nome varchar(10) ) as begin

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

create procedure [dbo].[sp_teste_loop] as begin

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

Upvotes: 3

Seibar
Seibar

Reputation: 70243

Define your temp table like this -

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

Then do this -

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

Upvotes: 34

Yves A Martin
Yves A Martin

Reputation: 411

I prefer using the Offset Fetch if you have a unique ID you can sort your table by:

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

This way I don't need to add fields to the table or use a window function.

Upvotes: 2

Sean
Sean

Reputation: 8787

This approach only requires one variable and does not delete any rows from @databases. I know there are a lot of answers here, but I don't see one that uses MIN to get your next ID like this.

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

Upvotes: 1

Control Freak
Control Freak

Reputation: 13213

Lightweight, without having to make extra tables, if you have an integer ID on the table

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

Upvotes: 4

Srinivas Maale
Srinivas Maale

Reputation: 11

Step1: Below select statement creates a temp table with unique row number for each record.

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

Step2:Declare required variables

DECLARE @ROWNUMBER INT
DECLARE @ename varchar(100)

Step3: Take total rows count from temp table

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

Step4: Loop temp table based on unique row number create in temp

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

Upvotes: 1

howmnsk
howmnsk

Reputation: 1

This is the code that I am using 2008 R2. This code that I am using is to build indexes on key fields (SSNO & EMPR_NO) n all tales

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

Upvotes: 0

OrganicCoder
OrganicCoder

Reputation: 117

This will work in SQL SERVER 2012 version.

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

Upvotes: 7

SReiderB
SReiderB

Reputation: 51

Another approach without having to change your schema or using temp tables:

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

Upvotes: 5

Syed Umar Ahmed
Syed Umar Ahmed

Reputation: 5952

-- [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

Upvotes: 3

Tim Lentine
Tim Lentine

Reputation: 7862

I agree with the previous post that set-based operations will typically perform better, but if you do need to iterate over the rows here's the approach I would take:

  1. Add a new field to your table variable (Data Type Bit, default 0)
  2. Insert your data
  3. Select the Top 1 Row where fUsed = 0 (Note: fUsed is the name of the field in step 1)
  4. Perform whatever processing you need to do
  5. Update the record in your table variable by setting fUsed = 1 for the record

  6. 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

Upvotes: 1

HLGEM
HLGEM

Reputation: 96552

I'm going to provide the set-based solution.

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

This is far faster than any looping techique and is easier to write and maintain.

Upvotes: 2

leoinfo
leoinfo

Reputation: 8195

Here is how I would do it:

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

[Edit] Because I probably skipped the word "variable" when I first time read the question, here is an updated response...

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

Upvotes: 19

Trevor
Trevor

Reputation: 501

This is how I do it:

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

No Cursors, no temporary tables, no extra columns. The USERID column must be a unique integer, as most Primary Keys are.

Upvotes: 50

dance2die
dance2die

Reputation: 36895

I really do not see the point why you would need to resort to using dreaded cursor. But here is another option if you are using SQL Server version 2005/2008
Use Recursion

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

Upvotes: 3

Wes Brown
Wes Brown

Reputation:

If you have no choice than to go row by row creating a FAST_FORWARD cursor. It will be as fast as building up a while loop and much easier to maintain over the long haul.

FAST_FORWARD Specifies a FORWARD_ONLY, READ_ONLY cursor with performance optimizations enabled. FAST_FORWARD cannot be specified if SCROLL or FOR_UPDATE is also specified.

Upvotes: 12

GateKiller
GateKiller

Reputation: 75869

You can use a while loop:

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

    Delete From #TempTable Where x = x
End

Upvotes: 4

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