Here's a few: - syntax highlighting - algebraic manipulations - optimization analysis of queries seen - analysis of equivalence of queries - query re

Here's a few: - syntax highlighting - algebraic manipulations - optimization analysis of queries seen - analysis of equivalence of queries - query rewriting (for style, performance, etc.) - RDBMS portability layer (implement a common subset of SQL, port queries to different engines; see previous item) I can probably think of more.