Select Statement

[Velen]

Hi,

I need to write up  a select statement something like:

Select a.supcode,a.code,b.desc,sum(c.qty),c.dept where a.supcode=b.supcode 
and a.code=c.code and a.code=b.code and c.dept between $tring1 and $tring2. 
group by supcode

This is fine but the problem is that there is duplicate supcode in a.

When running this query I often have c values which does not relate to 
supcode.

Anyone can help?

Thanks

Velen