Re: Proposal: is_castable

=?UTF-8?Q?Micha=C5=82_Wadas?= <michalwadas@gmail.com> writes:
> Currently there is no way to check if CAST will succeed.
> Therefore I propose adding new function: is_castable

> SELECT is_castable('foo' as time) // false

What would you actually do with it?

> Similar features are implemented in:
> - SQL Server (as TRY_CONVERT)
> - Oracle (as CONVERT([val] DEFAULT [expr] ON CONVERSION ERROR)

Somehow, I don't think those have the semantics of what you suggest here.

I suspect you are imagining that you could write something like

CASE WHEN is_castable(x as y) THEN cast(x as y) ELSE ...

but that will not work.  The THEN condition has to pass parse analysis
whether or not execution will ever reach it.

            regards, tom lane