How does one use loops in TSQL? - tsql

Question

In TSQL, I would like to change the following code from have to use hard coded dhomes to using a loop for optimization. My failed attempt at trying to add a loop is also included.
Declare #dhome Tinyint, #bp smallint, #lr smallint, #q smallint
// Set #dhome = 1
While(#dhome <= 3) // My attempt to add a loop
SELECT #lr = MAX(NQdDate), #q = NQd
FROM NQdHistory
WHERE dhomeId = #dhome
GROUP BY NQdDate, NQd
SELECT #bd = COUNT(*)
FROM bdhome
WHERE NQdDate= #lr AND dhomeID= #dhome
DELETE FROM ND1 WITH(XLOCK)
WHERE dhomeID= #dhome AND NQdDate= #lr
UPDATE NQdHistory
SET Nbd = #q - ##RowCount - #bp, NBd = #bp
WHERE NQdDate= #lr AND dhomeID= #dhome
Set #dhome = #dhome +1 //My attempt to end a loop

Answer 1

You're on the right track. You're missing your begin and end. Also, be sure to give #dhome a value. It looks like you started to and have it commented out on your third line:
Declare #dhome Tinyint, #bp smallint, #lr smallint, #q smallint
// Set #dhome = 1
While(#dhome <= 3) // My attempt to add a loop
begin
SELECT #lr = MAX(NQdDate), #q = NQd
FROM NQdHistory
WHERE dhomeId = #dhome
GROUP BY NQdDate, NQd
SELECT #bd = COUNT(*)
FROM bdhome
WHERE NQdDate= #lr AND dhomeID= #dhome
DELETE FROM ND1 WITH(XLOCK)
WHERE dhomeID= #dhome AND NQdDate= #lr
UPDATE NQdHistory
SET Nbd = #q - ##RowCount - #bp, NBd = #bp
WHERE NQdDate= #lr AND dhomeID= #dhome
Set #dhome = #dhome +1 //My attempt to end a loop
end
If you're familiar with C/C#/C++, think of T-SQL's Begin and End like curly braces { and }, if you're more familiar with VB Then and End If. Or more like pascals Begin and End. You get the idea :)

Answer 2

Missing a begin and end on your while.
WHILE (Transact-SQL)

Answer 3

Example 1
DECLARE #I INT,#COUNTVAR INT
SET #I = 1
DECLARE #Parent_Child TABLE(ID INT IDENTITY(1,1),ParentPositionID INT NULL,ChildPositionId Int)
INSERT INTO #Parent_Child(ParentPositionID,ChildPositionId)
SELECT DISTINCT PARENT_POSITION_ID,CHILD_POSITION_ID from tblPOSITION_HIERARCHY
--WHERE CHILD_POSITION_ID IN (--YOUR CONDITION IF ANY)
SELECT #COUNTVAR =COUNT(*) FROM #PTS_Parent_Child
DECLARE #int_SUPE_POSITION_ID INT, #int_CHILD_POSITION_ID INT
--loop through records here
WHILE #I <= #COUNTVAR
BEGIN
SELECT #int_SUPE_POSITION_ID=ParentPositionID,#int_CHILD_POSITION_ID=ChildPositionId FROM #Parent_Child WHERE ID=#I
--Whatever you want to do with records
SET #I=#I+1
END
Example 2
Just another approach if you are fine using temp tables.I have personally tested this and it will not cause any exception (even if temp table does not have any data.)
CREATE TABLE #TempTable
(
ROWID int identity(1,1) primary key,
HIERARCHY_ID_TO_UPDATE int,
)
--INSERT DATA INTO TEMP TABLE USING INSERT INTO CLAUSE OR FOR EAXMPLE BELOW
--INSERT INTO #TempTable VALUES(1)
--INSERT INTO #TempTable VALUES(2)
--INSERT INTO #TempTable VALUES(4)
--INSERT INTO #TempTable VALUES(6)
--INSERT INTO ##TempTable VALUES(8)
DECLARE #MAXID INT
SET #COUNTER =1
SELECT #MAXID=COUNT(*) FROM #TempTable
--PRINT #MAXID
WHILE (#MAXID > 0)
BEGIN
--DO THE PROCESSING HERE
SELECT #HIERARCHY_ID_TO_UPDATE =PT.HIERARCHY_ID_TO_UPDATE FROM #TempTable PT WHERE ROWID=#COUNTER
--PRINT '#MAXID VALUE '
--PRINT #MAXID
SET #MAXID=#MAXID-1
SET #COUNTER =#COUNTER + 1
End
If(OBJECT_ID('tempdb..#TempTable') IS NOT NULL)
BEGIN
DROP TABLE #TempTable
END