Re: How to quote the COALESCE function?

Hi

2016-03-29 10:30 GMT+02:00 Roman Scherer <roman(at)burningswell(dot)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 <gsievers19(at)comcast(dot)net>
> wrote:
>
>> Roman Scherer <roman(at)burningswell(dot)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(dot)consulting(at)comcast(dot)net
>> p: 312.241.7800
>>
>
>