How to write a foreach in SQL Server?

I am trying to achieve something along the lines of a for-each, where I would like to take the Ids of a returned select statement and use each of them.

DECLARE @i int
DECLARE @PractitionerId int
DECLARE @numrows int
DECLARE @Practitioner TABLE (
    idx smallint Primary Key IDENTITY(1,1)
    , PractitionerId int
)

INSERT @Practitioner
SELECT distinct PractitionerId FROM Practitioner

SET @i = 1
SET @numrows = (SELECT COUNT(*) FROM Practitioner)
IF @numrows > 0
    WHILE (@i <= (SELECT MAX(idx) FROM Practitioner))
    BEGIN

		SET @PractitionerId = (SELECT PractitionerId FROM @Practitioner WHERE idx = @i)

		--Do something with Id here
		PRINT @PractitionerId

        SET @i = @i + 1
    END

At the moment I have something that looks like the above, but am getting the error:

> Invalid column name 'idx'.

You seem to want to use a CURSOR. Though most of the times it's best to use a set based solution, there are some times where a CURSOR is the best solution. Without knowing more about your real problem, we can't help you more than that:

DECLARE @PractitionerId int

DECLARE MY_CURSOR CURSOR 
  LOCAL STATIC READ_ONLY FORWARD_ONLY
FOR 
SELECT DISTINCT PractitionerId 
FROM Practitioner

OPEN MY_CURSOR
FETCH NEXT FROM MY_CURSOR INTO @PractitionerId
WHILE @@FETCH_STATUS = 0
BEGIN 
	--Do something with Id here
	PRINT @PractitionerId
	FETCH NEXT FROM MY_CURSOR INTO @PractitionerId
END
CLOSE MY_CURSOR
DEALLOCATE MY_CURSOR

Suppose that the column PractitionerId is a unique, then you can use the following loop

DECLARE @PractitionerId int = 0
WHILE(1 = 1)
BEGIN
  SELECT @PractitionerId = MIN(PractitionerId)
  FROM dbo.Practitioner WHERE PractitionerId > @PractitionerId
  IF @PractitionerId IS NULL BREAK
  SELECT @PractitionerId
END

This generally (almost always) performs better than a cursor and is simpler:

DECLARE @PractitionerList TABLE(PracticionerID INT)
DECLARE @PracticionerID INT
    
INSERT @PractitionerList(PracticionerID)
SELECT PracticionerID
FROM Practitioner
    
WHILE(1 = 1)
BEGIN
    		
    SET @PracticionerID = NULL
    SELECT TOP(1) @PracticionerID = PracticionerID
    FROM @PractitionerList
    
    IF @PracticionerID IS NULL
    	BREAK
    		
    PRINT 'DO STUFF'
    
    DELETE TOP(1) FROM @PractitionerList
    
END

Your select count and select max should be from your table variable instead of the actual table

DECLARE @i int
DECLARE @PractitionerId int
DECLARE @numrows int
DECLARE @Practitioner TABLE (
	idx smallint Primary Key IDENTITY(1,1)
	, PractitionerId int
)

INSERT @Practitioner
SELECT distinct PractitionerId FROM Practitioner

SET @i = 1
SET @numrows = (SELECT COUNT(*) FROM @Practitioner)
IF @numrows > 0
	WHILE (@i <= (SELECT MAX(idx) FROM @Practitioner))
	BEGIN

		SET @PractitionerId = (SELECT PractitionerId FROM @Practitioner WHERE idx = @i)

		--Do something with Id here
		PRINT @PractitionerId

		SET @i = @i + 1
	END

I would say everything probably works except that the column idx doesn't actually exist in the table you're selecting from. Maybe you meant to select from @Practitioner:

WHILE (@i <= (SELECT MAX(idx) FROM @Practitioner))

because that's defined in the code above like that:

DECLARE @Practitioner TABLE (
    idx smallint Primary Key IDENTITY(1,1)
    , PractitionerId int
)

The following line is wrong in your version:

WHILE (@i <= (SELECT MAX(idx) FROM @Practitioner))

(Missing the @)

Might be an idea to change your naming convention so that the tables are more different.

Although cursors usually considered horrible evil I believe this is a case for FAST_FORWARD cursor - the closest thing you can get to FOREACH in TSQL.

Here is the one of the better solutions.

DECLARE @i int
			DECLARE @curren_val int
			DECLARE @numrows int
			create table #Practitioner (idx int IDENTITY(1,1), PractitionerId int)
			INSERT INTO #Practitioner (PractitionerId) values (10),(20),(30)
			SET @i = 1
			SET @numrows = (SELECT COUNT(*) FROM #Practitioner)
			IF @numrows > 0
			WHILE (@i <= (SELECT MAX(idx) FROM #Practitioner))
			BEGIN

				SET @curren_val = (SELECT PractitionerId FROM #Practitioner WHERE idx = @i)

				--Do something with Id here
				PRINT @curren_val
				SET @i = @i + 1
			END

> Here i've add some values in the table beacuse, initially it is empty.

We can access or we can do anything in the body of the loop and we can access the idx by defining it inside the table definition.

              BEGIN
				SET @curren_val = (SELECT PractitionerId FROM #Practitioner WHERE idx = @i)

				--Do something with Id here

				PRINT @curren_val
				SET @i = @i + 1
			END

I made a procedure that execute a FOREACH with CURSOR for any table.

Example of use:

CREATE TABLE #A (I INT, J INT)
INSERT INTO #A VALUES (1, 2), (2, 3)
EXEC PRC_FOREACH
    #A --Table we want to do the FOREACH
    , 'SELECT @I, @J' --The execute command, each column becomes a variable in the same type, so DON'T USE SPACES IN NAMES
   --The third variable is the database, it's optional because a table in TEMPB or the DB of the proc will be discovered in code

The result is 2 selects for each row. The syntax of UPDATE and break the FOREACH are written in the hints.

This is the proc code:

CREATE PROC [dbo].[PRC_FOREACH] (@TBL VARCHAR(100) = NULL, @EXECUTE NVARCHAR(MAX)=NULL, @DB VARCHAR(100) = NULL) AS BEGIN

	--LOOP BETWEEN EACH TABLE LINE            

IF @TBL + @EXECUTE IS NULL BEGIN
	PRINT '@TBL: A TABLE TO MAKE OUT EACH LINE'
	PRINT '@EXECUTE: COMMAND TO BE PERFORMED ON EACH FOREACH TRANSACTION'
	PRINT '@DB: BANK WHERE THIS TABLE IS (IF NOT INFORMED IT WILL BE DB_NAME () OR TEMPDB)' + CHAR(13)
	PRINT 'ROW COLUMNS WILL VARIABLE WITH THE SAME NAME (COL_A = @COL_A)'
	PRINT 'THEREFORE THE COLUMNS CANT CONTAIN SPACES!' + CHAR(13)
	PRINT 'SYNTAX UPDATE:

UPDATE TABLE
SET COL = NEW_VALUE
WHERE CURRENT OF MY_CURSOR

CLOSE CURSOR (BEFORE ALL LINES):

IF 1 = 1 GOTO FIM_CURSOR'
	RETURN
END
SET @DB = ISNULL(@DB, CASE WHEN LEFT(@TBL, 1) = '#' THEN 'TEMPDB' ELSE DB_NAME() END)

	--Identifies the columns for the variables (DECLARE and INTO (Next cursor line))

DECLARE @Q NVARCHAR(MAX)
SET @Q = '
WITH X AS (
	SELECT
		A = '', @'' + NAME
		, B = '' '' + type_name(system_type_id)
		, C = CASE
			WHEN type_name(system_type_id) IN (''VARCHAR'', ''CHAR'', ''NCHAR'', ''NVARCHAR'') THEN ''('' + REPLACE(CONVERT(VARCHAR(10), max_length), ''-1'', ''MAX'') + '')''
			WHEN type_name(system_type_id) IN (''DECIMAL'', ''NUMERIC'') THEN ''('' + CONVERT(VARCHAR(10), precision) + '', '' + CONVERT(VARCHAR(10), scale) + '')''
			ELSE ''''
		END
	FROM [' + @DB + '].SYS.COLUMNS C WITH(NOLOCK)
	WHERE OBJECT_ID = OBJECT_ID(''[' + @DB + '].DBO.[' + @TBL + ']'')
	)
SELECT
	@DECLARE = STUFF((SELECT A + B + C FROM X FOR XML PATH('''')), 1, 1, '''')
	, @INTO = ''--Read the next line
FETCH NEXT FROM MY_CURSOR INTO '' + STUFF((SELECT A + '''' FROM X FOR XML PATH('''')), 1, 1, '''')'

DECLARE @DECLARE NVARCHAR(MAX), @INTO NVARCHAR(MAX)
EXEC SP_EXECUTESQL @Q, N'@DECLARE NVARCHAR(MAX) OUTPUT, @INTO NVARCHAR(MAX) OUTPUT', @DECLARE OUTPUT, @INTO OUTPUT

	--PREPARE TO QUERY

SELECT
	@Q = '
DECLARE ' + @DECLARE + '
-- Cursor to scroll through object names
DECLARE MY_CURSOR CURSOR FOR
    SELECT *
    FROM [' + @DB + '].DBO.[' + @TBL + ']

-- Opening Cursor for Reading
OPEN MY_CURSOR
' + @INTO + '

-- Traversing Cursor Lines (While There)
WHILE @@FETCH_STATUS = 0
BEGIN
	' + @EXECUTE + '
    -- Reading the next line
    ' + @INTO + '
END
FIM_CURSOR:
-- Closing Cursor for Reading
CLOSE MY_CURSOR

DEALLOCATE MY_CURSOR'

EXEC SP_EXECUTESQL @Q --MAGIA
END

I came up with a very effective and (I think) readable way to do this.

1. Create a temp table and put the records you want to iterate in there

2. Use WHILE @@ROWCOUNT <> 0 to do the iterating

3. To get one row at a time do, SELECT TOP 1 <fieldnames>

   b. save the unique ID for that row in a variable

4. Do stuff, then delete the row from the temp table based on the ID saved at step 3b.

Here's the code. Sorry, its using my variable names instead of the ones in the question.

DECLARE @tempPFRunStops TABLE (
    ProformaRunStopsID int,
    ProformaRunMasterID int,
    CompanyLocationID int,
    StopSequence int
);

INSERT @tempPFRunStops (ProformaRunStopsID, ProformaRunMasterID, CompanyLocationID, StopSequence)
SELECT 
    ProformaRunStopsID, 
    ProformaRunMasterID, 
    CompanyLocationID, 
    StopSequence 
FROM ProformaRunStops
WHERE ProformaRunMasterID IN ( 
    SELECT ProformaRunMasterID 
    FROM ProformaRunMaster 
    WHERE ProformaId = 15 )

-- SELECT * FROM @tempPFRunStops

WHILE @@ROWCOUNT <> 0  -- << I dont know how this works
BEGIN
    SELECT TOP 1 * FROM @tempPFRunStops
    -- I could have put the unique ID into a variable here
    
    SELECT 'Ha'  -- Do Stuff
    
    DELETE @tempPFRunStops 
    WHERE ProformaRunStopsID = (SELECT TOP 1 ProformaRunStopsID FROM @tempPFRunStops)
END