[samus]

A problem is that SQL does not cleanly map to what the DBMS does to execute it. For simple queries, this is exactly the point. For more complex queries, the SELECT-FROM-WHERE straightjacket feels quite restrictive though.

The abstraction really hurts when you have to optimize slow queries and convince the optimizer to do it the right way. Entering the query plan (essentially, the annotated AST of an expression of relational algrebra) would often be helpful.

Also, SQL is ultimately text. This makes it very cumbersome to build tools that dynamically assemble queries, like ORMs or customized search dialogs, and to insert parameters. Parser performance impact overall DBMS performance quite a bit, and it would be useful to reduce overhead there too.

[uvdn7]

Yep, every abstraction introduced has added cost, in some cases. The fastest way of executing a program is to build special hardware with the perfect state changes of a set of transistors — I am not joking.