Null Result Returned Even Though IS NOT NULL Specified.

Hi guys,

I've got a query on a particular table returning an odd result:

SELECT DISTINCT WorkStation
FROM Invoice
WHERE WorkStation Is Not Null
ORDER BY WorkStation

This query returns the rows I'd expect plus a null row. This doesn't happen in databases at other sites, or in other tables at this site. The following query behaves as I'd expect returning only non-null AccountNumbers.

SELECT DISTINCT AccountNumber
FROM Suppliers
WHERE AccountNumber Is Not Null
ORDER BY AccountNumber

I can't reproduce these results on another site on a table of the same structure, or on another table at this site.

Any suggestions as to what might be going on?

Pertinent info:
---
select @@Version

Microsoft SQL Server 2000 - 8.00.760 (Intel X86)
Dec 17 2002 14:22:05 Copyright (c) 1988-2003 Microsoft Corporation
Standard Edition on Windows NT 5.2 (Build 3790: Service Pack 1)
---
dbcc checkdb
Abridged result:
CHECKDB found 0 allocation errors and 0 consistency errors in database 'POS'.
---
SELECT * INTO #Inv FROM Invoice

SELECT DISTINCT WorkStation
FROM #Inv
WHERE WorkStation Is Not Null
ORDER BY WorkStation

Does not reproduce this problem (and so is a probable fix) but the questions remains, what causes this?

TIA,
Karl.