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.
来源：https://stackoverflow.com/questions/26595394/what-kind-of-language-is-sql