I already wrote about search in a couple of posts, and these features of ChessBase and Chess Assistant are surprisingly still essentially unchanged and relevant:
Online tactics: Find Sacrifices feature in Chessbase Light
Chess Assistant feature - Search for current pawn structure and material
Since then I found two more interesting search features:
1) SCID has this pawn structure search that I was not aware of:
2) Also Chessbase has relatively recently added an ability to search for similar pawn structures.
Still, you can’t directly search for IQP with Chessbase, and it seems that only Chessbase allows to search for sacrifices (if you are aware of other programs that can do that – please leave a comment!). That’s why we have more than one chess database software …