In my humble opinion, there are so many proprietary and / or nonstandard extensions to SQL that it's turned into a right mess. I think that the language itself is a bit kludgey and it'd be much easier if it'd just correspond to relational algebra directly. (Eg if you do a select * from foo where x = y, you're actually doing two operations, a select and a filter, and the natural language like syntax of the language makes it very ambiguous and confusing when you're dealing with complicated structures like nested joins and such)