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SQL Server, Subqueries and data types

Today I had to deal with an issue on SQL Server 2005 that I thought might be worth sharing. Maybe someone else runs into a similar issue and can't figure out why SQL Server is playing stupid.

I was trying to run a query similar to the one below, it was generated by a reporting tool:

select sum(a11.COGS_ORDERED), 
sum(a11.LINE_RECEIVED)
from 
(SELECT 
ID
, COGS_ORDERED
, QTY_SHORTED
, 'LINE_RECEIVED' =
 CASE
   WHEN QTY_SHORTED = 0 THEN 1
   ELSE 0
 END
FROM myTable a11)

SQL Server always returned the error message "Arithmetic overflow error converting expression to data type int." . I figured out that the issue has to do with my case statement so I tested to run a sum right on the case statement and it worked fine:


SELECT 
SUM( CASE
   WHEN QTY_SHORTED = 0 THEN 1
   ELSE 0
 END)
FROM myTable a11


After doing some research I found out that SQL Server stores the result of the subquery as int and is not able to convert it to bigint when doing the SUM. Forcing a convert already in the case statement fixes the issue:

select sum(a11.COGS_ORDERED), 
sum(a11.LINE_RECEIVED)
from 
(SELECT 
ID
, COGS_ORDERED
, QTY_SHORTED
, 'LINE_RECEIVED' =
 CASE
   WHEN QTY_SHORTED = 0 THEN CONVERT(BIGINT,1)
   ELSE CONVERT(BIGINT,0)
 END
FROM myTable a11)

I think a database management system should be smart enough to do this conversion by itself.

Comments

Pravesh Singh said…
Very informative post, you explain very well on SubQuery in SQL server. I've some good articles too which I was found during searching this topic over internet. Here I'm sharing that post links........
http://www.mindstick.com/Blog/202/Sub%20query%20in%20sqlserver

http://www.dbtalks.com/UploadFile/rohatash123/495/

I'm very thankful for your nice post.

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