T-SQL Query Join on different column depending on case - sql

Question

I have a legacy system that has a sales table and a customer table, CMS and CUST respectively. I need to query for the shipped to address based on different criteria. The customer table treats each address as its own customer. So if I have a billing address, then a shipping address, those will both be different CUSTNUM's. The CMS table has columns CUSTNUM and SHIPNUM. If the sales order uses the billing address as the shipping address, SHIPNUM = 0. If those 2 address are different, SHIPNUM = a different customer number than CUSTNUM. I'm trying to write a query that joins CUST to CMS based on the case of SHIPNUM being > 0 or not. My original query just used CUSTNUM, and ignored the SHIPNUM. My new query is syntactically correct and executes, but the row count returned is 2860 vs 3590 for the old query. The old join statement is just the commented out line :ON CMS.CUSTNUM = CUST.CUSTNUM.
from
KGI_LOTNOS as LOT
INNER JOIN CMS
ON LOT.ORDERNO = CMS.ORDERNO
JOIN CUST
ON CUST.CUSTNUM =
CASE
WHEN CMS.SHIPNUM > 0
THEN CMS.SHIPNUM
Else CMS.CUSTNUM
END
-- ON CMS.CUSTNUM = CUST.CUSTNUM
INNER JOIN COUNTRY as C
ON CUST.COUNTRY = C.COUNTRY
Here is an example from the CMS table;
CUSTNUM SHIPNUM ORDERNO
41863 77394 828509 <--Different billing and shipping address
43242 69291 776888 <--Different billing and shipping address
2356 0 765022 <--Same billing and shipping address
Any thoughts on how to make this work?
PS Here is the original query in its entirety.
select
CUST.CUSTNUM as Customer,
CMS.CUSTNUM,
CMS.SHIPNUM,
CUST.CTYPE,
CMS.ORDERNO,
CMS.ODR_DATE,
LTRIM(RTRIM(CUST.FIRSTNAME)) as First,
LTRIM(RTRIM(CUST.LASTNAME)) as Last,
LTRIM(RTRIM(CUST.COMPANY)) as Company,
LTRIM(RTRIM(CUST.PHONE)) as Phone,
LTRIM(RTRIM(CUST.EMAIL)) as Email,
LTRIM(RTRIM(CUST.ADDR)) as ADDR1,
LTRIM(RTRIM(CUST.ADDR2)) as ADDR2,
LTRIM(RTRIM(CUST.ADDR3)) as ADDR3,
LTRIM(RTRIM(CUST.CITY)) as City,
LTRIM(RTRIM(CUST.State)) as State,
LTRIM(RTRIM(CUST.ZIPCODE)) as Zip,
LTRIM(RTRIM(C.NAME)) as Country,
LOT.ITEMNO,
LOT.LOTNO,
COUNT(LOT.ITEMNO) as Quantity
from
KGI_LOTNOS as LOT
INNER JOIN CMS
ON LOT.ORDERNO = CMS.ORDERNO
LEFT JOIN CUST
ON CMS.CUSTNUM = CUST.CUSTNUM
INNER JOIN COUNTRY as C
ON CUST.COUNTRY = C.COUNTRY
where
(
CUST.CTYPE IN ('P','W','Z')
)
AND
(
LOT.LOTNO IN ('1000001','20001','300001')
)
GROUP BY
CMS.ORDERNO,
CUST.CUSTNUM,
CMS.CUSTNUM,
CMS.SHIPNUM,
CUST.CTYPE,
CUST.FIRSTNAME,
CMS.ODR_DATE,
CUST.LASTNAME,
CUST.COMPANY,
CUST.PHONE,
CUST.EMAIL,
CUST.ADDR,
CUST.ADDR2,
CUST.ADDR3,
LOT.ITEMNO,
CUST.CITY,
CUST.STATE,
CUST.ZIPCODE,
C.NAME,
LOT.LOTNO
ORDER BY
Customer,
CMS.ORDERNO,
LOT.ITEMNO,
LOT.LOTNO

Answer 1

If you use INNER JOIN you have risk to exclude raws which have no reference in another table. This could be caused by any of 2 another joins in your expression - comment them and try again. If you still receive less records you should check consistency of your data - one table has values which not correspond to values in another table.
BTW, I don't like CASE in JOIN expression simply because it looks ugly. What do you thinK about this expression which seemed to do the job too:
LEFT JOIN CUST
ON CUST.CUSTNUM = COALESCE(NULLIF(CMS.SHIPNUM, 0), CMS.CUSTNUM)

Answer 2

You could use a CTE like this.
WITH cte (ORDERNO, SHIPNUM) AS
(
SELECT ORDERNUM, SHIPNUM = CASE
WHEN CMS.SHIPNUM > 0
FROM CMS

Answer 3

Fewer records join using your altered criteria, there are some CMS.SHIPNUM values that don't have matching CUSTNUM in the CUST table.
To find the problematic entries change from INNER to OUTER join and add WHERE criteria, something like:
LEFT JOIN CUST
ON CUST.CUSTNUM = CASE WHEN CMS.SHIPNUM > 0 THEN CMS.SHIPNUM
ELSE CMS.CUSTNUM
END
WHERE CUST.CUSTNUM IS NULL
AND CMS.SHIPNUM > 0
Edit: You'll have to remove the INNER JOIN to COUNTRY to see the unmatched from your updated JOIN since it joins on a field from the customer table, and make sure to have the SHIPNUM field in your SELECT.

Answer 4

your query looks correct but not sure why it is not working, try left joinCUST table twiceone on shipping and the other on billing and then write the case statement for each customer column.
select
LTRIM(RTRIM(case when CMS.SHIPNUM > 0 THEN CUST.FIRSTNAME else CUST_BILL.FIRSTNAME end )) as First,
from
KGI_LOTNOS as LOT
INNER JOIN CMS
ON LOT.ORDERNO = CMS.ORDERNO
left JOIN CUST CUST
ON CUST.CUSTNUM = CMS.SHIPNUM
left JOIN CUST CUST_BILL
ON CMS.CUSTNUM = CUST_BILL.CUSTNUM
INNER JOIN COUNTRY as C
ON CUST.COUNTRY = C.COUNTRY
if it still outputs less rows then something else is wrong