On Sun, Feb 20, 2022 at 12:31:22PM +0200, Markur Sens wrote:
> >
> > Maybe you could rely on some old grammar hack to have something a bit similar,
> > as (expr).funcname is an alias for funcname(expr). For instance:
>
> Is this documented & expected behavior or it’s just happens to work?
I don't think it's documented but it's an expected behavior, see
https://github.com/postgres/postgres/blob/master/src/backend/parser/parse_func.c#L57-L88
/*
* Parse a function call
*
* For historical reasons, Postgres tries to treat the notations tab.col
* and col(tab) as equivalent: if a single-argument function call has an
* argument of complex type and the (unqualified) function name matches
* any attribute of the type, we can interpret it as a column projection.
* Conversely a function of a single complex-type argument can be written
* like a column reference, allowing functions to act like computed columns.
*
* If both interpretations are possible, we prefer the one matching the
* syntactic form, but otherwise the form does not matter.
*
* Hence, both cases come through here. If fn is null, we're dealing with
* column syntax not function syntax. In the function-syntax case,
* the FuncCall struct is needed to carry various decoration that applies
* to aggregate and window functions.
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