The Internals of PostgreSQL
Part 3.1.1 is about the parser, which uses lex and yacc. I actually used it as a source to convince a professor to let us use lex and yacc to build our lexer and parser for a SQL engine for a DB implementation class I took. His expectations were a bit unrealistic for what a bunch of seniors would be able to accomplish in three weeks in C (other similar level of difficulty classes and job searching weigh a real burden), and he initially said no to me asking if we could use lex and yacc. Postgres's source made a convincing enough argument. Gave me a reason to learn lex and yacc, as well as making a much easier to modify parser. I wrote the parser for my group, and we were the only group that finished the parser in time, and at all.Just an anecdote with some fond memories that were made possible by Postgres and its internals. Postgres has a place in my heart for that, and being a damn fine DB of course!