Re: [GENERAL] Puzzled by UNION with iso-8859-1 types

Ken Tanzer <ken.tanzer@gmail.com> writes:
> Hi.  I've solved my practical problems, and I know unknown types are
> just bad, but am still curious about why some of these cause errors,
> and others don't.

> ag_consulting=> SELECT * FROM (SELECT '1'::unknown) foo UNION ALL
> SELECT * FROM (SELECT '1'::unknown) bar;
> ERROR:  failed to find conversion function from unknown to text

FWIW, this succeeds in 9.5 and up, as a result of more aggressive
application of the rule "coerce an unknown value to text if we cannot
find any other interpretation".

> ag_consulting=> CREATE TEMP TABLE t1 AS SELECT '1'::unknown; \d t1
> WARNING:  column "unknown" has type "unknown"
> DETAIL:  Proceeding with relation creation anyway.
> SELECT 1
>      Table "pg_temp_2.t1"
>  Column  |  Type   | Modifiers
> ---------+---------+-----------
>  unknown | unknown |

As of v10, this will produce a table with a column of type text,
not type unknown, again as a result of more aggressively forcing
unknown to be something else.
        regards, tom lane


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