Re: : Re: A strange problem
От | Ragnar Hafstað |
---|---|
Тема | Re: : Re: A strange problem |
Дата | |
Msg-id | 1125239931.22356.5.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Re: : Re: A strange problem (Tang Tim Hei <timheit@netvigator.com>) |
Список | pgsql-general |
On Sun, 2005-08-28 at 16:22 +0800, Tang Tim Hei wrote: > The following commands are little different from the previous one. > (1) select A.* from test.currency A, test.price_list B where A.curr_cd=B.curr_cd and A.curr_cd='USD' > (2) select A.* from test.currency A, test.price_list B, test.country C where A.curr_cd=B.curr_cd and A.curr_cd='USD' > > For command (1), it is ok. The result is what I expect. > However, for command (2), it has problem. I added the "test.country C" to it, > here I actually just write a table name to it and no more other purpose. I do not understand what you mean by that. the added table name means an additional cartesian join > However, the result maybe totally different. that is because of the added cartesian join > If the table "country" is not empty, the result is just the same as in command (1) it will only be the same if the table contains EXACTLY 1 row > but if "country" is empty, there are no result row. a cartesian join to 0 rows results in 0 rows if you are talking about something else, please show us a concrete simple example. gnari
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