How to Loop Through a Table Variable in T-Sql

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

Add an identity to your table variable, and do an easy loop from 1 to the @@ROWCOUNT of the INSERT-SELECT.

Try this:

DECLARE @RowsToProcess  int
DECLARE @CurrentRow     int
DECLARE @SelectCol1     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

SET @CurrentRow=0
WHILE @CurrentRow<@RowsToProcess
BEGIN
    SET @CurrentRow=@CurrentRow+1
    SELECT 
        @SelectCol1=col1
        FROM @table1
        WHERE RowID=@CurrentRow

    --do your thing here--

END

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

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).

Using cursor to loop through a table variable in SQL Server

This uses two parts - first convert your string into a table, then do bulk inserts into your destination. No need for cursors.

** Please excuse any syntax errors as I'm doing it without access to your actual tables or functions so cant test it, but you get the idea

declare @in varchar(max)
set @in= '1/1/2018-2/1/2018,2/1/2018-3/1/2018,3/1/2018-4/1/2018,4/1/2018-5/1/2018,5/1/2018-6/1/2018,6/1/2018-7/1/2018,7/1/2018-8/1/2018,8/1/2018-9/1/2018,9/1/2018-10/1/2018,10/1/2018-11/1/2018,11/1/2018-12/1/2018,12/1/2018-12/31/2018'

declare @xml xml;
set @xml= convert(xml,'<r><f>'+replace(replace(@in,',','</t></r><r><f>'),'-','</f><t>') +'</t></r>')

declare @t table(id int identity, f date, t date)
insert @t
select 
    Tbl.Col.value('f[1]', 'date') f, 
    Tbl.Col.value('t[1]', 'date') t
FROM  @xml.nodes('//r') Tbl(Col) 

select * from @t

declare @count int;
select @count=count(*) from @t

INSERT INTO #BidAverageCycleCalculation (SortOrder, Code, Data)
select id, 'SL Payroll',(select dbo.GetAverageCycleBetweenBids(f,t,'SL')) from @t

INSERT INTO #BidAverageCycleCalculation (SortOrder, Code, Data)
select id+@count,'GV Payroll',(select dbo.GetAverageCycleBetweenBids(f,t,'GV')) from @t

INSERT INTO #BidAverageCycleCalculation (SortOrder, Code, Data)
select id+@count*2,'Global Payroll',(select dbo.GetAverageCycleBetweenBids(f,t,'GVS')) from @t

INSERT INTO #BidAverageCycleCalculation (SortOrder, Code, Data)
select id+@count*3,'TimeHCM',(select dbo.GetAverageCycleBetweenBids(f,t,'Time')) from @t

Loop through table by row T-SQL

I suggest to rewrite it using Cursors as follows faster:

DECLARE @IMAX INT,
        @ICOUNT INT,
        @INTERFACE_ID_36 INT,
        @INTERFACE_ID_38 INT

DECLARE db_cursor CURSOR FOR  
SELECT Interface_ID FROM INTERFACE_36_DATA  

OPEN db_cursor   
FETCH NEXT FROM db_cursor INTO @INTERFACE_ID_36   

WHILE @@FETCH_STATUS = 0   
BEGIN
       SELECT @INTERFACE_ID_36
       -- All your other selects  

       FETCH NEXT FROM db_cursor INTO @INTERFACE_ID_36   
END   

CLOSE db_cursor   
DEALLOCATE db_cursor

Loop through table while records keep getting added to the table

I'd use a do while loop instead.

Have a variable called moreToProcess data type boolean.

Set the value before entering the loop using execute SQL statement based on count > 0

First step in the loop is to get a record to process using exec SQL.

Before exiting loop rerun the SQL to reset the variable.

Set to loop while moreToProcess is true.

t-sql for loop to iterate through tables

You could try this:

DECLARE @Table TABLE
(
TableName VARCHAR(50),
Id int identity(1,1)
)

INSERT INTO @Table
Select table_name From INFORMATION_SCHEMA.COLUMNS 
Where column_name = 'fieldA'

DECLARE @max int
DECLARE @SQL VARCHAR(MAX) 
DECLARE @TableName VARCHAR(50)
DECLARE @id int = 1

select @max = MAX(Id) from @Table

WHILE (@id <= @max)
BEGIN

SELECT @TableName = TableName FROM @Table WHERE Id = @id
SET @SQL =     'alter table '+ @TableName +' add new_col varchar(8);
                update '+ @TableName + ' set new_col = old_col;'
PRINT(@SQL)  --COMMENT THIS LINE OUT AND COMMENT IN THE NEXT EXEC(@SQL) IF YOU SEE THE CORRECT OUTPUT
--EXEC(@SQL)
SET @id = @id +1
END

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