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

Answer 1

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 2

My two cents.. From KM.'s answer, if you want to drop one variable, you can do a countdown on @RowsToProcess instead of counting up.

DECLARE @RowsToProcess  int;

DECLARE @table1 TABLE (RowID int not null primary key identity(1,1), col1 int )  
INSERT into @table1 (col1) SELECT col1 FROM table2
SET @RowsToProcess = @@ROWCOUNT 

WHILE @RowsToProcess > 0 -- Countdown
BEGIN
    SELECT *
        FROM @table1
        WHERE RowID=@RowsToProcess

    --do your thing here--

    SET @RowsToProcess = @RowsToProcess - 1; -- Countdown
END

Answer 3

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.

Answer 4

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 5

Select Top 1 can easily resolve it without the need of any sequence/order.

Create Function Test_Range()
Returns
@Result Table (ID Int)
As
Begin

Declare @ID Varchar(10) = ''
Declare @Rows Int, @Row Int = 0
Declare @Num Int, @RangeTo Int

Declare @RangeTable Table (ID Varchar(10), RangeFrom Int, RangeTo Int)
Insert Into @RangeTable Values ('A', 1, 10)
Insert Into @RangeTable Values ('B', 25,30)

Set @Rows = (Select Count(*) From @RangeTable)

While @Row <= @Rows
Begin
    Set @Row = @Row + 1
    Select Top 1 @ID = ID, @Num = RangeFrom, @RangeTo = RangeTo  From @RangeTable
    Where ID > @ID
    While @Num <= @RangeTo
    Begin
        Insert Into @Result Values (@Num)
        Set @Num = @Num + 1
    End
End
Return
End