Re: [HACKERS] _text problem in union

Zakkr <zakkr@zf.jcu.cz> writes:
> abil=> select '{"aaa"}'::_text union select '{"bbb"}'::_text;
> ERROR:  Unable to identify an ordering operator '<' for type '_text'
>         Use an explicit ordering operator or modify the query

Depending on what you're trying to do, UNION ALL might be an adequate
workaround.  UNION is defined to remove duplicates, so it has to sort
the results of the union'ed queries, which requires an ordering
operator.  UNION ALL just appends the two query results together...

In the long run we probably ought to think about providing ordering
operators for array types.
        regards, tom lane