I had written a piece of code about two years ago that used the aggregate feature of PostgreSQL to create an array of integers from an aggregate, as:
select int_array_aggregate( column ) from table group by column
While it seems pointless to create an array on a select, it has a purpose in OLAP. For instance, suppose you do this:
create table fast_lookup as select reference, int_array_aggregate(result) from table group by result
The "fast_lookup" table now has all the result entries as an array in a single row. In the systems that I have used this, it has provided a dramatic improvement, especially when you have a high number of identical "reference" entries in a classic "one to many" table.
The question is, would a more comprehensive solution be wanted? Possible? Something like:
create table fast_lookup as select reference, aggregate_array( field ) from table group by field
Where the function aggregate_array takes any number of data types.
Any thoughts? I think I need to fix the code in the current /contrib/intagg anyway, so is it worth doing the extra work to included multiple data types?
It's also useful in conjunction with statistically processing. There is a array_accum function in PL/R; I just made a post to the SQL list the other day on this.
(http://archives.postgresql.org/pgsql-sql/2003-03/msg00124.php)
Here's the meat of it:
CREATE OR REPLACE FUNCTION array_accum (_name, name) RETURNS name[] AS '$libdir/plr','array_accum' LANGUAGE 'C';
CREATE AGGREGATE accumulate ( sfunc = array_accum, basetype = name, stype = _name );
regression=# SELECT accumulate(tablename) as cruft FROM pg_tables WHERE tablename LIKE 'c%';
cruft
---------------------------------------
{connectby_int,connectby_text,ct,cth}
(1 row)
See: http://www.joeconway.com/plr/doc/plr-aggregate-funcs.html and download at: http://www.joeconway.com/plr/
I'd be happy to split the array functions out of PL/R and sumbit them to PATCHES if there is any interest.
Joe
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