WOW, that's messy. Someone did some bad design decisions.
Instead of conditional filters, you have to play with logic.
Instead of
or if(p.PartNoAlias='',,w.PartNoAlias=p.PartNoAlias))
You could use
OR (p.PartNoAlias != '' AND w.PartNoAlias=p.PartNoAlias))
Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?
How to post data/code on a forum to get the best help: Option 1 / Option 2