Building a cross-language compute serialization
It may surprise you to know that SQL execution engines don't actually execute SQL directly! (Or you may already know this, in which case, good job!) Under the hood of your favorite query engine, what happens is that it parses the query into some intermediate representation of the query and executes that. There are multiple reasons for this:
- It's really hard to optimize a SQL query directly and be sure that you haven't changed the semantics of what it is doing. Translating to an intermediate representation allows for easier, programmatic optimizations that are guaranteed to be equivalent to the original query.
- Abstracting the specific query language (ANSI SQL versus other dialects) from the execution reduces the impact that changes to the language have on the execution engine. As long as the same intermediate representation is created by the parser, it doesn't matter what changes in the query language. ...
