Re: Understanding "unknown" data type

Steve Crawford <scrawford(at)pinpointresearch(dot)com> writes:
> On 04/07/2011 11:29 AM, Tom Lane wrote:
>> Steve Crawford<scrawford(at)pinpointresearch(dot)com> writes:
>>> 1. Where can I read up on the purpose and properties of a data-type of
>>> unknown?

>> It's the type initially imputed to unadorned string literals and NULL...

> Is there a place in the documentation that explains this? I haven't
> found it so far.

Probably not --- it's normally just an implementation detail.

>> ...It can be cast to anything, but that's a hardwired behavior not
>> something listed in pg_cast.

> Hmmm. Not *anything* - at least not directly:

Unadorned string literals and NULL constants can be cast to anything.
Once it's not a simple constant anymore, you can't do anything at all
with it.

regards, tom lane