NULL value in subselect in UNION causes error

Jan Wieck <JanWieck@Yahoo.com> writes:

Checked it against HEAD and 8.2:
postgres=# select 1, 1, 1 union select * from (select 2, null, 2) two;
ERROR: failed to find conversion function from "unknown" to integer

It's always done that. The SQL spec would tell you that you have to
cast the null to some specific type. We allow untyped nulls in contexts
where we can derive a type from reasonably nearby context, but an
integer two levels up and over in another union arm isn't very nearby
IMHO. So I'm not particularly concerned about making this work ...

regards, tom lane

On 1/26/2007 3:41 PM, Tom Lane wrote:

Jan Wieck <JanWieck@Yahoo.com> writes:

Checked it against HEAD and 8.2:
postgres=# select 1, 1, 1 union select * from (select 2, null, 2) two;
ERROR: failed to find conversion function from "unknown" to integer

It's always done that. The SQL spec would tell you that you have to
cast the null to some specific type. We allow untyped nulls in contexts
where we can derive a type from reasonably nearby context, but an
integer two levels up and over in another union arm isn't very nearby
IMHO. So I'm not particularly concerned about making this work ...

That explains. Thanks.

Jan

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