From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | sszabo(at)bigpanda(dot)com |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] correlated subquery |
Date: | 1999-12-30 00:44:07 |
Message-ID: | 199912300044.TAA16571@candle.pha.pa.us |
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Lists: | pgsql-hackers |
>
> >Is this a good example of a required correlated subquery:
> >
> > SELECT f1.firstname, f1.lastname, f1.age
> > FROM friends f1
> > WHERE age = (
> > SELECT MAX(age)
> > FROM friends f2
> > WHERE f1.state = f2.state
> > )
> > ORDER BY firstname, lastname
> >
> >It finds the oldest person in each state. HAVING can't do that, right?
>
> I'm assuming that this is for the book... If so, you might want to also
> note that this query can return more people than there are states if
> multiple people in the same state have the maximum age for that state.
>
> I'm not sure how deeply you are going into this, but getting only one
> person per state looks like it might be fairly painful... You might be
> able cheat if there was only one field besides age and state in the output
> using group by and an aggregate.
Yikes, that would be painful. Good point. Fortunately, the data has
only one max person per state.
--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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