Victor Yegorov <vyego...@gmail.com> writes: > Well, for `varchar` type Postgres is able to do `varchar` -> `bpchar` cast > for my constant. I do not understand why for `text` it cannot and casts > column instead.
In cross-type comparisons like these, the parser basically has a choice between whether to apply texteq or bpchareq. It's going to have to cast one side or the other either way. It prefers to cast to text, not away from text, because text is the preferred type in the string category. So "bpchar = text" is resolved as texteq. In the "bpchar = varchar" case, that doesn't happen because neither side is text to start with, so bpchareq is chosen on the grounds of requiring fewer casts. There's no varchareq operator (because varchar just relies on text's operators). If there were, you'd probably get an "ambiguous operator, please cast" error from "bpchar = varchar", because neither of those are preferred types so there would be no way to prefer one interpretation over the other. Similarly, if text weren't treated as a preferred type then "bpchar = text" would just fail, it would still not be resolved the way you want. See http://www.postgresql.org/docs/9.5/static/typeconv-oper.html for a more detailed explanation. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
