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Re: Question on collapsing a sparse matrix

From: David Gardner <david(at)gardnerit(dot)net>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Question on collapsing a sparse matrix
Date: 2009-04-27 20:19:41
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
Take a look into the crosstab function in the tablefunc contrib module.

Might be able to do what you are describing.

Bryan Emrys wrote:
> I've been handed a table that reminds me of a sparse matrix and I'm 
> thinking that there should be some SQL way to simplify it.
> Assume table like (a column for every department, separate rows for 
> each state if any department has headcount in the state, but each row 
> has only one headcount entry):
> State    Dept1   Dept2   Dept3   Dept4
> AZ          3         NULL    NULL    NULL
> AZ        NULL       2        NULL    NULL
> AZ        NULL     NULL     17       NULL
> CA          2         NULL    NULL    NULL
> CA        NULL       21      NULL    NULL
> CA        NULL     NULL   NULL      6
> CA        NULL     NULL     4         NULL
> etc
> I'm trying to get to          
> State    Dept1   Dept2   Dept3   Dept4
> AZ          3           2           17      NULL
> CA          2         21             4        6
> etc
> Is there some way of rolling up or ANDing records so that I can sum 
> each state into a single record per state? This looks like something 
> that would be obvious, but I'm apparently missing it. Any pointers 
> would be appreciated.
> (BTW, there are a couple hundred departments in the actual table, they 
> are not conveniently numbered and as you may guess from the example, 
> there is not a consistent number of rows for each state; some have 
> only 1 row, some have 40 or more, it simply depends on how many 
> departments have headcount in that state.)
> Bryan 

David Gardner

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