问题:

Is SQL a context free language or some other type of language?

回答1:

According to https://stackoverflow.com/a/31265136 SQL is not a regular language. The short explanation is that each select query looks like

 SELECT x FROM y WHERE z

and y can be another select query itself, so it cannot be simulated with finite-state machine. As mentioned before, there are some CFGs for SQL standarts in Backus–Naur Form, thereby SQL is nonregular context free language.

回答2:

@aquinas wrote:

Do you mean is SQL also regular? CFG's encompass regular languages. So, they aren't mutually exclusive. To answer your question though, SQL is not a regular language.

@MSX wrote:

Just to clarify, a language is context-free when it is generated by a context-free grammar. There're SQL context-free grammar definitions online. Just google around and you'll find some. Here's one, for example.