Thanks Tom.
On 04/07/2011 11:29 AM, Tom Lane wrote:
Steve Crawford<scrawford@xxxxxxxxxxxxxxxxxxxx> 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.
...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:
steve=# create table foobar as select '1' as somedata;
WARNING: column "somedata" has type "unknown"
DETAIL: Proceeding with relation creation anyway.
SELECT 1
^
steve=# select somedata::int from foobar;
ERROR: failed to find conversion function from unknown to integer
...
steve=# create table foobar as select '2011-04-07' as somedata;
WARNING: column "somedata" has type "unknown"
DETAIL: Proceeding with relation creation anyway.
SELECT 1
steve=# select somedata::date from foobar;
ERROR: failed to find conversion function from unknown to date
Throwing an error has been discussed, but it seems likely to break
things for some people.
A GUC? (Like we need more of those :))
...but there aren't terribly bad side-effects
(other than not being able to operate on that table column). The
cases that are of practical interest tend to involve label columns in
views.
Not sure how the variety of front-ends might behave when fed an
"unknown". It's pretty easy to accidentally create such a column and
have it lurking waiting to cause downstream trouble.
For now, I have a daily alert script that warns me if a dev has
accidentally done this.
Cheers,
Steve
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