=?utf-8?q?PG_Doc_comments_form?= <nore...@postgresql.org> writes: > https://www.postgresql.org/docs/9.6/static/sql-select.html
> The last line for <from_item> breaks the group. There should be something > like: > <from_item> > <join_from> > <simple_from> > (with better naming). Hm, I can't get excited about it. You're correct that the grammar as stated is ambiguous, and if we introduced another level of nonterminal we could make it reflect the left-to-right precedence of join operators ... but I think 99% of our users would just find it more confusing that way. The existing statement in the text that "In the absence of parentheses, JOINs nest left-to-right" is probably clearer to most people than a formal grammar for it would be. (Heck, even our actual bison grammar file relies on precedence to define this behavior, rather than an extra nonterminal ... and you can't get much nerdier than a bison grammar.) regards, tom lane