SQL是哪种语言? [英] What kind of language is SQL?

问题描述

SQL是上下文无关语言还是某种其他类型的语言?

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

推荐答案

根据 https://stackoverflow.com/a/31265136 SQL不是常规语言.简短的解释是每个选择查询看起来像

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

和y本身可以是另一个选择查询，因此无法使用有限状态机进行模拟.如前所述， Backus–Naur表单，因此SQL是非常规上下文免费语言.

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.

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