SQL CASE WHEN to narrow results, change field - sql

Question

I've read dozens of answers regarding CASE and am not sure that is what i need to be using here, it seems like it should work but its not:
Data:
OrderNum OrderLine PartNum
200011 1 ABC-1
200011 2 DEF-1
200012 1 XYZ-1
What I would like to return:
OrderNum Item#
200011 MIXED
200012 XYZ-1
What I am returning instead:
OrderNum Item#
200011 ABC-1
200011 MIXED
200012 XYZ-1
My query:
SELECT OrderHed.OrderNum,
(CASE WHEN ShipDtl.OrderLine > '1' then 'MIXED' else ShipDtl.PartNum end) as [Item#]
FROM dbo.OrderHed, dbo.ShipDtl
WHERE ShipDtl.Company = OrderHed.Company
AND ShipDtl.OrderNum = OrderHed.OrderNum
GROUP BY OrderHed.OrderNum, ShipDtl.OrderLine, ShipDtl.Part

Answer 1

Try with grouping like
SELECT OrderHed.OrderNum,
(CASE WHEN SUM(ShipDtl.OrderLine) > 1 then 'MIXED' else MAX(ShipDtl.PartNum) end) as [Item#]
FROM dbo.OrderHed, dbo.ShipDtl
WHERE ShipDtl.Company = OrderHed.Company
AND ShipDtl.OrderNum = OrderHed.OrderNum
GROUP BY OrderHed.OrderNum
SQLFiddle Demo : http://sqlfiddle.com/#!3/209d8/1

Answer 2

You didn't write which database engine you use, but if it is SQL 2005 and above, I'd think using the window function for COUNT will make things easier as you then do not need to group.
SELECT DISTINCT
OrderHed.OrderNum ,
CASE
WHEN COUNT(ShipDtl.OrderLine) OVER (PARTITION BY ShipDtl.OrderNum) > 1 THEN 'MIXED'
ELSE PartNum
END AS [Item#]
FROM dbo.OrderHed ,
dbo.ShipDtl
WHERE ShipDtl.Company = OrderHed.Company
AND ShipDtl.OrderNum = OrderHed.OrderNum
You'll need to DISTINCT though, because it'll select a row per line, but each order with multiple lines will be MIXED, so you can easily distinct.
This will simply select the OrderNum and if multiple orderlines exists per ordernum Count(xxx) OVER (partition by yyy) it'll select 'MIXED', otherwise the partnum.
And then distinct the result.

Answer 3

There is no compulsion to use CASE (is there?).
In your example, CASE is being used to perform logical OR. There are other ways of performing logical OR in SQL e.g. UNION:
WITH T
AS
(
SELECT OrderHed.OrderNum, ShipDtl.PartNum, ShipDtl.OrderLine
FROM dbo.OrderHed, dbo.ShipDtl
WHERE ShipDtl.Company = OrderHed.Company
AND ShipDtl.OrderNum = OrderHed.OrderNum
)
SELECT OrderNum, PartNum
FROM T
WHERE OrderLine = 1
AND OrderNum NOT IN (
SELECT OrderNum
FROM T T2
WHERE OrderLine > 1
)
UNION
SELECT OrderNum, 'MIXED' AS PartNum
FROM T
WHERE OrderLine > 1;