Re: Pet Peeves?
От | Octavio Alvarez |
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Тема | Re: Pet Peeves? |
Дата | |
Msg-id | 1233446050.5647.73.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Re: Pet Peeves? (Gregory Stark <stark@enterprisedb.com>) |
Ответы |
Re: Pet Peeves?
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Список | pgsql-general |
On Sat, 2009-01-31 at 23:36 +0000, Gregory Stark wrote: > Octavio Alvarez <alvarezp@alvarezp.ods.org> writes: > > > A crosstab is not but a presentational transform of the data set. Any > > information you would eventually need can be taken from the original > > data source, one way or another. That's why dynamic-column crosstab are > > not a problem, and the DBMS should not worry about providing the > > information about the columns, maybe by simply not allowing the > > dynamic-column ones in subqueries. > > What about a WHERE clause like > > WHERE P1 > P2 You could either: (1) do "FROM grades AS g1 INNER JOIN grades AS g2 ON g1.P1 > g2.P2", generating the record set before applying the crosstab transformation. (2) Since you are implying the existence of P1 and P2, use the fixed-number-of-columns crosstab case instead, for which PG would actually be able to give the column definitions without running the query, and after that, joining the results with some other query.
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