Joshua Ma <josh@xxxxxxxxxxxxx> writes: > Our team is upgrading from 9.4 to 9.5, and we noticed this behavior change: > 9.5: > # SELECT true = true = true; > ERROR: syntax error at or near "=" > LINE 1: SELECT true = true = true; > Now, there's actually a larger problem with this, since it's not actually > chained equality and only looks like it. It looks like 9.4 is evaluating > right-to-left. We're going to fix usages of this to instead do (a = b && a > = c) instead of (a = b = c). > However, I wanted to email in because I couldn't see what in the 9.5 > changelog (https://www.postgresql.org/docs/9.6/static/release-9-5.html) > would cause this to syntax error. This is a consequence of commit c6b3c939b "Make operator precedence follow the SQL standard more closely", which removed the former "%right '='" grammar declaration. That caused "a = b = c" to be parsed as "a = (b = c)", which was surprising, and wouldn't work at all unless a was boolean. Now "=" is declared %nonassoc, so that if you actually want behavior like that, you need to write some parens. But it seems much more likely that people writing that are making a mistake. We discussed the associativity-of-= issue in the thread leading up to that patch, https://www.postgresql.org/message-id/flat/12603.1424360914%40sss.pgh.pa.us but I evidently forgot to mention this detail in the commit log message, so it didn't get into the release notes either. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general