Get CASE statement to work with column names that are aggregates

Below I have attached the Query and the Result Set and my attempt at the CASE function.

In the result set you'll see it returns
  the Qty of a product available in stock as QtyInStock
  AND the Qty that was ordered as 'QtyOrdered'.
I want to have another column called 'QtyToDeliver' which works like this:
If
   QtyInStock < QtyOrdered
THEN
   QtyToDeliver = QtyInStock
ELSE
  QtyToDeliver = QtyOrdered

With my CASE function like it is I get error:
Incorrect syntax near '<'.
or
Invalid column name 'QtyInStock'.

====================================
==THE RESULTSET
====================================
PRODUCT_ID  QtyInStock QtyOrdered
1032        1          1
1016        10         1
1018        0          1

==========================
===THE QUERY
==========================
SELECT
  Product.PRODUCT_ID,
  IsNull(Count(Stock.STOCK_ID),0) As QtyInStock,
  (SELECT 
     TRANS_CLIENT_STOCK.QTY 
   FROM 
     TRANS_CLIENT_STOCK
   WHERE 
     TRANS_CLIENT_STOCK.TC_ID = 94403 
     AND TRANS_CLIENT_STOCK.PRODUCT_ID = Product.PRODUCT_ID) AS QtyOrdered
--,
--QtyToDeliver = CASE QtyInStock
--WHEN QtyInStock < QtyOrdered THEN QtyOrdered
--ELSE QtyOrdered
--END
FROM
  Product
    LEFT JOIN Stock
      ON Product.PRODUCT_ID = Stock.PRODUCT_ID
      AND Stock.CLIENT_ID = 691
      AND POS_ID IS NULL
      AND PickedDate IS NULL 
WHERE
  PRODUCT.PRODUCT_ID NOT IN
   (Select PRODUCT_ID FROM EXT_TYPE) 
Group by
  Product.PRODUCT_ID,
  Product.SortOrder 
order by
  Product.SortOrder

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LVL 13
rfwoolfAsked:
Who is Participating?
 
cyberkiwiConnect With a Mentor Commented:
SELECT PRODUCT_ID, QtyInStock, QtyOrdered,
QtyToDeliver = CASE
WHEN QtyInStock < QtyOrdered THEN QtyOrdered
ELSE QtyOrdered
END
FROM
(
SELECT
  Product.PRODUCT_ID,
  Product.SortOrder,
  IsNull(Count(Stock.STOCK_ID),0) As QtyInStock,
  (SELECT
     TRANS_CLIENT_STOCK.QTY
   FROM
     TRANS_CLIENT_STOCK
   WHERE
     TRANS_CLIENT_STOCK.TC_ID = 94403
     AND TRANS_CLIENT_STOCK.PRODUCT_ID = Product.PRODUCT_ID) AS QtyOrdered
FROM
  Product
    LEFT JOIN Stock
      ON Product.PRODUCT_ID = Stock.PRODUCT_ID
      AND Stock.CLIENT_ID = 691
      AND POS_ID IS NULL
      AND PickedDate IS NULL
WHERE
  PRODUCT.PRODUCT_ID NOT IN
   (Select PRODUCT_ID FROM EXT_TYPE)
Group by
  Product.PRODUCT_ID,
  Product.SortOrder
) SQ
order by
  SortOrder
0
 
Dale BurrellDirectorCommented:
, QtyToDeliver = CASE WHEN QtyInStock < QtyOrdered THEN QtyOrdered ELSE QtyOrdered END
0
 
rfwoolfAuthor Commented:
dale_burrell>

Msg 207, Level 16, State 1, Line 14
Invalid column name 'QtyInStock'.
Msg 207, Level 16, State 1, Line 14
Invalid column name 'QtyOrdered'.
Msg 207, Level 16, State 1, Line 14
Invalid column name 'QtyOrdered'.
Msg 207, Level 16, State 1, Line 15
Invalid column name 'QtyOrdered'.
0
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rfwoolfAuthor Commented:
..as you can see, QtyInStock is an aggregate column, maybe that's the problem? :
  IsNull(Count(Stock.STOCK_ID),0) As QtyInStock,
0
 
rfwoolfAuthor Commented:
Thanks cyberkiwi... I don't know if anyone's ever pointed out that you seem to be pretty good at this stuff :)
Can you confirm though that you agree this is because QtyInStock was part of an aggregate function or something.. now that you've taken the CASE statement out of the main result set, it works no problem ??
0
 
cyberkiwiConnect With a Mentor Commented:
It is not so much aggregate or not, it is the fact that it is a derived column.
Aggregation makes a column, so do functions like dateadd and expressions like field+3 etc.

You have two choices - repeat the entire expression (not friendly given one of them is a subquery) or put the whole query into a subquery.

Regards
0
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