Re: Why is a union of two null-results automatically casted to type text ?
От | Tom Lane |
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Тема | Re: Why is a union of two null-results automatically casted to type text ? |
Дата | |
Msg-id | 3328.1087323609@sss.pgh.pa.us обсуждение исходный текст |
Ответ на | Re: Why is a union of two null-results automatically casted to type text ? (Frank van Vugt <ftm.van.vugt@foxi.nl>) |
Ответы |
Re: Why is a union of two null-results automatically casted to type text ?
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Список | pgsql-general |
Frank van Vugt <ftm.van.vugt@foxi.nl> writes: >> UNION requires assignment of a definite type to the inputs, because >> otherwise there's no certainty that we know how to identify distinct >> and non-distinct values. The alternative to assigning TEXT is to >> reject the inner UNION outright :-( > But in a UNION ALL the distinctiveness isn't an issue, is it? True. We do not currently distinguish UNION from UNION ALL as far as datatype assignment rules go (INTERSECT/EXCEPT also act just the same). In theory we could allow an output column of UNION ALL to remain "unknown". I'm not sure if it'd be a good idea to do so or not. It'd make this particular example work the way you want, but otherwise it seems like making UNION ALL a special case would be a bit of a wart on the type system. regards, tom lane
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