Re: [SQL] PgSQL 6.5.1 and Group BY pb
От | Albert REINER |
---|---|
Тема | Re: [SQL] PgSQL 6.5.1 and Group BY pb |
Дата | |
Msg-id | 19990825225141.B159@frithjof обсуждение исходный текст |
Ответ на | Re: [SQL] PgSQL 6.5.1 and Group BY pb (Herouth Maoz <herouth@oumail.openu.ac.il>) |
Список | pgsql-sql |
On Wed, Aug 25, 1999 at 03:58:29PM +0300, Herouth Maoz wrote: > At 14:08 +0300 on 25/08/1999, Giampiero Raschetti wrote: ... > In fact, the above seems to indicate that you are not well aware of what > joins are, or at least you don't know that you have to restrict them to > make sense of your data. You really have to add WHERE g.id = u.id. Of course this is not at the core of Giampiero's problem, but there are instances where you don't use a restriction, i.e. exactly when you want to get the Cartesian product of the tables. Suppose, e.g., that you want to generate a list of all the fields on a chess board. You can do this by create table rows (l char); create table cols (n int2); insert into rows ('a'); ... (all the way to 'h') insert into cols (1); ... (all the way to 8); select l, n from rows, cols; Albert. -- --------------------------------------------------------------------------- Post an / Mail to / Skribu al: Albert Reiner<areiner@tph.tuwien.ac.at> ---------------------------------------------------------------------------
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