How to convert this Access inner join query into SQL Server? - sql

Question

I want to write an update statement that compares the new code table to the old code by joining on the MASTER_ID. Then If the NEW_CODE.CODE = 1234 AND OLD_CODE.CODE_ID is not in the CODE_MAPPING table then SET NEW_CODE.CODE_ID = OLD_CODE.CODE_ID AND NEW_CODE.SEQ_NO = OLD_CODE.SEQ_NO. This is what I have so far but it does not seem to correctly update if I get a null value in the CODE_ID column. I think I need to do a self join but nothing I do seems to work any help would be greatly appreciated.
I have three tables with the following data:
**NEW_CODE**
MASTER_ID SEQ_NO CODE_ID CODE
100 0 XX 1234
200 0 5555
300 0 XX 1234
300 0 XX 1234
**OLD_CODE**
MASTER_ID SEQ_NO CODE_ID
100 1 D1
200 1 A1
300 1
300 2 Z1
**CODE_MAPPING**
CODE_ID
A1
B1
C1
D1
UPDATE STATEMENT:
UPDATE NEW
SET SEQ_NO = OLD.SEQ_NO,
CODE_ID = OLD.CODE_ID
FROM NEW_CODE NEW
INNER JOIN OLD_CODE OLD
ON NEW.MASTER_ID = OLD.MASTER_ID
LEFT JOIN CODE_MAPPING CM
ON OLD.CODE_ID = CM.CODE_ID
WHERE NEW.CODE = 1234
AND CM.CODE_ID IS NULL
The updated table should look like this:
**UPDATED NEW_CODE**
MASTER_ID SEQ_NO CODE_ID CODE
100 0 XX 1234
200 0 5555
300 1 1234
300 2 Z1 1234
So the only thing that should update is the two rows with a MASTER_ID of 300. But for some reason I am getting the following result instead:
**CURRENT RESULT NEW_CODE**
MASTER_ID SEQ_NO CODE_ID CODE
100 0 XX 1234
200 0 5555
300 2 Z1 1234
300 2 Z1 1234

Answer 1

As you have two rows with same identifier (MASTER_ID), tsql is needed instead of a simple statement.
Precondition for rows to update:
Every row in NEW could be matched to one row in OLD and reverse.
We need a criteria to identify updated rows in NEW. I use SEQ_NO=0 here.
a unique key for each row in OLD and NEW is needed. Your example data don't contain a unique key. So I add one to OLD and one to NEW. It can be dropped in the end.
alter table OLD add IDX int IDENTITY(1,1)
alter table NEW add IDX int IDENTITY(1,1)
declare a cursor on OLD (only rows to be updated)
DECLARE #IdxOld int
DECLARE #IdxNew int
DECLARE MY_CURSOR CURSOR
LOCAL STATIC READ_ONLY FORWARD_ONLY
FOR
SELECT idx
FROM OLD
WHERE NOT EXISTS (SELECT * FROM CODE_MAPPING CM
WHERE OLD.CODE_ID = CM.CODE_ID)
do foreach on OLD and update NEW
OPEN MY_CURSOR
FETCH NEXT FROM MY_CURSOR INTO #IdxId
WHILE ##FETCH_STATUS = 0
BEGIN
SELECT #IdxNew = Min(Idx) -- min to get only one row
FROM NEW
INNER JOIN OLD_CODE OLD ON NEW.MASTER_ID = OLD.MASTER_ID
WHERE NEW.CODE = 1234
AND OLD.IDX = #IdxOld -- current row from old
AND SEQ_NO=0 -- row not updated yet
UPDATE NEW
SET SEQ_NO = OLD.SEQ_NO,
CODE_ID = OLD.CODE_ID
FROM NEW_CODE NEW
INNER JOIN OLD_CODE OLD ON NEW.MASTER_ID = OLD.MASTER_ID
WHERE NEW.IDX = #IdxNew
AND OLD.IDX = #IdxOld
FETCH NEXT FROM MY_CURSOR INTO #IdxId
END
CLOSE MY_CURSOR
DEALLOCATE MY_CURSOR
Drop IDX columns
alter table OLD drop COLUMN IDX
alter table NEW drop COLUMN IDX

Answer 2

The aliases do not match in the update . . . that is new is not new_code. Try this:
UPDATE NC
SET SEQ_NO = OC.SEQ_NO,
CODE_ID = OC.CODE_ID
FROM NEW_CODE NC INNER JOIN
OLD_CODE OC
ON NC.MASTER_ID = OC.MASTER_ID LEFT JOIN
CODE_MAPPING CM
ON OC.CODE_ID = CM.CODE_ID
WHERE NC.CODE = 1234 AND CM.CODE_ID IS NULL;