From: Tom Lane <tgl@sss.pgh.pa.us>
To: sgarden@club.fr
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: the date() function is undocumented while quite necessary
Date: Sat, 15 Feb 2020 11:36:50 -0500
Message-ID: <18379.1581784610@sss.pgh.pa.us> (raw)
In-Reply-To: <158177916388.6746.12385265846339386100@wrigleys.postgresql.org>
References: <158177916388.6746.12385265846339386100@wrigleys.postgresql.org>
PG Doc comments form <noreply@postgresql.org> writes:
> I can't find anywhere the documentation of the SQL DATE() function which
> extracts the date part out of a timestamp.
It's a type cast written in function-like syntax, as documented in
https://www.postgresql.org/docs/current/sql-expressions.html#SQL-SYNTAX-TYPE-CASTS
We don't really encourage that notation, because it's confusing
and it doesn't work for every possible type name, which is why
you won't find it mentioned very many places.
> Please note that according to my tests, one can't use the cast operator when
> defining expression-based indexes, while the date(column) expression is
> accepted.
You can if you put parentheses around it:
regression=# create table t1 (f1 timestamp);
CREATE TABLE
regression=# create index on t1 (f1::date);
ERROR: syntax error at or near "::"
LINE 1: create index on t1 (f1::date);
^
regression=# create index on t1 ((f1::date));
CREATE INDEX
This is per the restriction explained in the CREATE INDEX docs, that
any expression-to-be-indexed that doesn't look like a function call
requires parentheses.
https://www.postgresql.org/docs/current/indexes-expressional.htmlhttps://www.postgresql.org/docs/current/sql-createindex.html
regards, tom lane
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To: pgsql-docs@postgresql.org
Cc: tgl@sss.pgh.pa.us, sgarden@club.fr, pgsql-docs@lists.postgresql.org
Subject: Re: the date() function is undocumented while quite necessary
In-Reply-To: <18379.1581784610@sss.pgh.pa.us>
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