Hi 2016-03-29 10:30 GMT+02:00 Roman Scherer <ro...@burningswell.com>:
> Tom, Jerry, I'm going to do the same as the `quote_identifier` > function of Postgres does, only quote if necessary. > > Thanks for your explanation, Roman. > The coalesce is one few functions implemented by special rule in PostgreSQL parser. Some functions with special behave, special syntax are implemented differently than other functions:coalesce, xmlelement, least, greatest, current_timestamp, session_user. When you use "coalesce", then PostgreSQL try to search custom function named coalesce. These functions are not usually in pg_proc catalogue. see https://github.com/postgres/postgres/blob/master/src/backend/parser/gram.y func_expr_common_subexpr Regards Pavel > > > On Tue, Mar 29, 2016 at 1:31 AM, Jerry Sievers <gsiever...@comcast.net> > wrote: > >> Roman Scherer <ro...@burningswell.com> writes: >> >> > Hello, >> > >> > I'm building a DSL in Clojure for SQL and specifically PostgreSQL >> > [1]. When building a SQL statement that contains a function call >> > I always quote the function name with \" in case the function >> > name contains any special characters. Here's an example: >> > >> > (select db ['(upper "x")]) >> > ;=> ["SELECT \"upper\"(?)" "x"] >> > >> > This worked fine so far, but today I found a case that doesn't >> > work as expected, the COALESCE function. >> > >> > (select db ['(coalesce nil 0)]) >> > ;=> ["SELECT \"coalesce\"(NULL, 0)"] >> > >> > Can someone explain to me what's the difference between quoting >> > the `upper` and the `coalesce` function? I can execute the >> > following statements via psql, and it works as expected: >> > >> > SELECT upper ('x'); >> > SELECT "upper"('x'); >> > SELECT coalesce(NULL, 1); >> > >> > But as soon as I try this with `coalesce` I get an error: >> > >> > SELECT "coalesce"(NULL, 1); >> >> >> While not a precise answer to your question, it may be of interest to >> note that coalesce is *not* a function. >> >> It is a language construct with a function-like syntax. >> >> select distinct proname from pg_proc where proname in ('coalesce', >> 'lower'); >> proname >> --------- >> lower >> (1 row) >> >> > >> > ERROR: function coalesce(unknown, integer) does not exist >> > LINE 1: SELECT "coalesce"(NULL, 1); >> > ^ >> > HINT: No function matches the given name and argument types. You >> might need to add explicit type casts. >> > >> > What I found so far is, that the `upper` function can be found in >> > the `pg_proc` table but not `coalesce`. >> > >> > SELECT proname FROM pg_proc WHERE proname ILIKE 'upper'; >> > SELECT proname FROM pg_proc WHERE proname ILIKE 'coalesce'; >> > >> > Does this mean that `coalesce` isn't a classical function and I >> > shouldn't quote it? Is it instead a keyword, as described in >> > the "Lexical Structure" section of the docs [2]? How can I find >> > out which other functions are not meant to be quoted? >> > >> > I'm aware that I do not need to quote the `coalesce` and `upper` >> > functions and I may change my strategy for quoting functions names. >> > >> > Thanks for you help, Roman. >> > >> > [1] https://github.com/r0man/sqlingvo >> > [2] >> http://www.postgresql.org/docs/current/static/sql-syntax-lexical.html >> > >> >> -- >> Jerry Sievers >> Postgres DBA/Development Consulting >> e: postgres.consult...@comcast.net >> p: 312.241.7800 >> > >
