Re: ANSI join types
От | Tom Lane |
---|---|
Тема | Re: ANSI join types |
Дата | |
Msg-id | 4807.1029300953@sss.pgh.pa.us обсуждение исходный текст |
Ответ на | ANSI join types (Bruce Momjian <pgman@candle.pha.pa.us>) |
Список | pgsql-docs |
Bruce Momjian <pgman@candle.pha.pa.us> writes: > Also, I can not find documentation on UNION JOINS in our docs. There is none because we don't support it. While I took the trouble to make the parser take it, there's no implementation. I'm not now excited about making it happen ever, because I read this in SQL99: Annex D Deprecated features It is intended that the following features will be removed at a later date from a revised version of this part of ISO/IEC 9075: 1) The ability to specify UNION JOIN in a <joined table> has been deprecated. BTW, I think the description > * Union: This is different than the UNION operator used to merge the > output of multiple queries. This is the inverse of an Inner, only > rows are returned when no matches are found is pretty poor. As near as I can tell from the SQL92 spec, "x UNION JOIN y" is supposed to produce the same result as (select *,<y.nulls> from x) UNION ALL (select <x.nulls>,* from y) where <y.nulls> denotes a list of NULLs matching the columnset of y, and similarly for <x.nulls>. This behavior has nothing to do with whether any value matches exist between x and y --- it makes no join comparisons at all. regards, tom lane
В списке pgsql-docs по дате отправления: