Can I loop through a table variable in T-SQL?

Question

Is there anyway to loop through a table variable in T-SQL?

DECLARE @table1 TABLE ( col1 int )  
INSERT into @table1 SELECT col1 FROM table2

I use cursors as well, but cursors seem less flexible than table variables.

DECLARE cursor1 CURSOR  
    FOR SELECT col1 FROM table2  
OPEN cursor1  
FETCH NEXT FROM cursor1

I would like to be able to use a table variable in the same manner as a cursor. That way I could execute some query on the table variable in one part of the procedure, and then later execute some code for each row in the table variable.

Any help is greatly appreciated.

Answer 1

You can loop through the table variable or you can cursor through it. This is what we usually call a RBAR - pronounced Reebar and means Row-By-Agonizing-Row.

I would suggest finding a SET-BASED answer to your question (we can help with that) and move away from rbars as much as possible.

Answer 2

look like this demo:

DECLARE @vTable TABLE (IdRow int not null primary key identity(1,1),ValueRow int);

-------Initialize---------
insert into @vTable select 345;
insert into @vTable select 795;
insert into @vTable select 565;
---------------------------

DECLARE @cnt int = 1;
DECLARE @max int = (SELECT MAX(IdRow) FROM @vTable);

WHILE @cnt <= @max
BEGIN
    DECLARE @tempValueRow int = (Select ValueRow FROM @vTable WHERE IdRow = @cnt);

    ---work demo----
    print '@tempValueRow:' + convert(varchar(10),@tempValueRow);
    print '@cnt:' + convert(varchar(10),@cnt);
    print'';
    --------------

    set @cnt = @cnt+1;
END

Version without idRow, using ROW_NUMBER

    DECLARE @vTable TABLE (ValueRow int);
-------Initialize---------
insert into @vTable select 345;
insert into @vTable select 795;
insert into @vTable select 565;
---------------------------

DECLARE @cnt int = 1;
DECLARE @max int = (select count(*) from @vTable);

WHILE @cnt <= @max
BEGIN
    DECLARE @tempValueRow int = (
        select ValueRow 
        from (select ValueRow
            , ROW_NUMBER() OVER(ORDER BY (select 1)) as RowId 
            from @vTable
        ) T1 
    where t1.RowId = @cnt
    );

    ---work demo----
    print '@tempValueRow:' + convert(varchar(10),@tempValueRow);
    print '@cnt:' + convert(varchar(10),@cnt);
    print'';
    --------------

    set @cnt = @cnt+1;
END

Answer 3

Here is my version of the same solution...

    declare @id int

        SELECT @id = min(fPat.PatientID)
        FROM tbPatients fPat
        WHERE (fPat.InsNotes is not null AND DataLength(fPat.InsNotes)>0)

while @id is not null
begin
    SELECT fPat.PatientID, fPat.InsNotes
    FROM tbPatients fPat
    WHERE (fPat.InsNotes is not null AND DataLength(fPat.InsNotes)>0) AND fPat.PatientID=@id

    SELECT @id = min(fPat.PatientID)
    FROM tbPatients fPat
    WHERE (fPat.InsNotes is not null AND DataLength(fPat.InsNotes)>0)AND fPat.PatientID>@id

end

Answer 4

Here's another answer, similar to Justin's, but doesn't need an identity or aggregate, just a primary (unique) key.

declare @table1 table(dataKey int, dataCol1 varchar(20), dataCol2 datetime)
declare @dataKey int
while exists select 'x' from @table1
begin
    select top 1 @dataKey = dataKey 
    from @table1 
    order by /*whatever you want:*/ dataCol2 desc

    -- do processing

    delete from @table1 where dataKey = @dataKey
end

Answer 5

Here's my variant. Pretty much just like all the others, but I only use one variable to manage the looping.

DECLARE
  @LoopId  int
 ,@MyData  varchar(100)

DECLARE @CheckThese TABLE
 (
   LoopId  int  not null  identity(1,1)
  ,MyData  varchar(100)  not null
 )


INSERT @CheckThese (YourData)
 select MyData from MyTable
 order by DoesItMatter

SET @LoopId = @@rowcount

WHILE @LoopId > 0
 BEGIN
    SELECT @MyData = MyData
     from @CheckThese
     where LoopId = @LoopId

    --  Do whatever

    SET @LoopId = @LoopId - 1
 END

Raj More's point is relevant--only perform loops if you have to.

Answer 6

DECLARE @table1 TABLE (
    idx int identity(1,1),
    col1 int )

DECLARE @counter int

SET @counter = 1

WHILE(@counter < SELECT MAX(idx) FROM @table1)
BEGIN
    DECLARE @colVar INT

    SELECT @colVar = col1 FROM @table1 WHERE idx = @counter

    -- Do your work here

    SET @counter = @counter + 1
END

Believe it or not, this is actually more efficient and performant than using a cursor.