Re: Count column with name 'count' returns multiple rows. Why?

On 2017-08-18 06:37:15 -0500, Justin Pryzby wrote:
> On Fri, Aug 18, 2017 at 01:01:45PM +0200, Rob Audenaerde wrote:
> > I don't understand why this query:
> >
> > select count(base.*) from mytable base;
> >
> > does return multiple rows.
> >
> > select count(1) from mytable base;
> >
> > returns the proper count.
> >
> > There is a column with the name 'count'.
> >
> > Can anyone please explain this behaviour?
>
> https://www.postgresql.org/docs/9.6/static/sql-expressions.html#SQL-EXPRESSIONS-FUNCTION-CALLS
> https://www.postgresql.org/docs/9.6/static/rowtypes.html#ROWTYPES-USAGE

Maybe I overlooked it, but I don't see anything in those pages which
explains why «count» is parsed as a column name in the first example and
as a function name in the second.

Nor do I see what «count(base.*)» is supposed to mean. It seems to be
completely equivalent to just writing «count», but the part in
parentheses is not ignored: It has to be either the table name or the
table name followed by «.*». Everything else I tried either led to a
syntax error or to «count» being recognized as a function. So apparently
columnname open-parenthesis tablename closed-parenthesis is a specific
syntactic construct, but I can't find it documented anywhere.

hp

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