Re: Cast jsonb to numeric, int, float, bool

On Mon, Mar 12, 2018 at 12:43:20PM -0400, Tom Lane wrote:
> Another fundamental problem is that implicit casts mask mistakes.
> If there's an implicit cast to numeric, that applies everywhere not
> only where it was what you meant.  For some context on this you might
> go back to the archives around the time of 8.3, where we actually
> removed a bunch of implicit casts because they led to too many
> surprising behaviors.  Restricting implicit casts to the same type
> category is a rule-of-thumb for reducing the potential surprise
> factor.

+1 to that.

>> What would be other options, if not implicit cast?
>
> Explicit casts, ie (jsonvar->'fieldname')::numeric.  Yeah, you have
> to write a bit more, but you don't get surprised by the way the
> parser interpreted your query.
>
> The other thing you can potentially do is use a variant operator
> name, as we did for text output with ->>.  But that doesn't scale
> to very many result types, because it's impossible to choose
> readily mnemonic operator names.  So I'd stick with the casts.

And +1 to that.  Implicit casts are cool things when they don't cause a
potential loss of precision, which could be equivalent to losing some
data, so sticking with casts looks more acceptable to me, and I would
vote to not move on with this patch.
--
Michael