This paper mainly presents the principles of LEX and YACC and gives the BNF of select sentence. Using these tools,we can implement the lexical and syntax analysis of SQL select sentence and generate the syntax analysis tree.

• 介绍了LEX、YACC的基本工作原理 ,给出了SQL查询语句的BNF范式 ,利用这两个工具实现了对SQL查询语句的词法分析和语法分析 ,并生成语法分析树