A line like SELECT name FROM users WHERE id = 1 is just text when the client sends it. The first thing the backend does after receiving it is figure out "what do these characters mean." This chapter covers the second of the five stages we saw in 1.1.1: the parser and analyzer. By the time this stage finishes, the SQL text has been transformed twice. First into a raw parse tree that captures the grammatical structure, then into a Query tree with meaning attached after consulting the catalog. The catalog, in case you need a refresher, is the set of internal tables that PostgreSQL keeps to describe itself. Which tables exist, what columns they have, what argument types each function accepts, what data types are defined: all of it lives as rows in these tables. PostgreSQL treats user data and metadata uniformly, both as ordinary tables. The raw stage looks only at form (does this follow SELECT syntax, where are the IDENTs).…