Re: Question on collapsing a sparse matrix

Take a look into the crosstab function in the tablefunc contrib module.
http://www.postgresql.org/docs/8.3/static/tablefunc.html

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