- range_agg 1.2.1
- Merge adjacent/overlapping ranges
There are three forms, depending on whether or not you want to permit gaps & overlaps.
If you call
range_agg(anyrange) (with just a single range parameter),
then it will raise an error if a gap or overlap is detected,
and on success it will return a single range.
You call also call
range_agg(r anyrange, permit_gaps boolean, permit_overlaps boolean),
and it will return an array of ranges.
It will still merge adjacent/overlapping ranges as much as possible,
but it will add a new array element whenever there is a gap.
So if your group had these ranges:
[2018-07-01,2018-07-15) [2018-07-15,2018-07-31) [2018-09-01,2018-09-15)
Then you would get back:
You can also choose to raise an exception
on either an overlap or a gap,
by setting the respective parameter to
Finally there is a two-param version,
range_agg(r anyrange, permit_gaps boolean),
which will raise on overlaps but permits gaps (if passed
This is likely most useful for coalescing rows in a temporal table (see below).
With temporal databases
The primary motivation of this extension is to let you "coalesce" rows in a temporal database,
as described in section 6.5.2 of Snodgrass's book
Developing Time-Oriented Database Applications in SQL.
You can use the three-param version of the function to permit gaps
(still forbidding overlaps if you like),
UNNEST on the resulting range array, like so:
SELECT room_id, t2.booked_during FROM ( SELECT room_id, range_agg(booked_during, true) AS booked_during FROM reservations GROUP BY room_id ) AS t1, UNNEST(t1.booked_during) AS t2(booked_during) ORDER BY room_id, booked_during ; room_id | booked_during ---------+------------------------- 1 | [07-01-2018,07-14-2018) 1 | [07-20-2018,07-22-2018) 2 | [07-01-2018,07-03-2018) 5 | [07-01-2018,07-03-2018) 6 | [07-01-2018,07-10-2018) 7 | [07-01-2018,07-14-2018) (6 rows)
There is a small caveat about using custom range types.
The one-parameter version of
range_agg will support them automatically,
but the two- and three-parameter versions take a little more work.
Postgres has no way to declare a function that takes
anyrange and returns
so we have separate declarations for
Out of the box we support all built-in range types.
If you want to support a new one, e.g.
inetrange, just run these commands
(after creating the extension):
CREATE OR REPLACE FUNCTION range_agg_transfn(internal, inetrange, boolean) RETURNS internal AS 'range_agg', 'range_agg_transfn' LANGUAGE c IMMUTABLE; CREATE OR REPLACE FUNCTION range_agg_finalfn(internal, inetrange, boolean) RETURNS inetrange AS 'range_agg', 'range_agg_finalfn' LANGUAGE c IMMUTABLE; CREATE AGGREGATE range_agg(inetrange, boolean) ( stype = internal, sfunc = range_agg_transfn, finalfunc = range_agg_finalfn, finalfunc_extra ); CREATE OR REPLACE FUNCTION range_agg_transfn(internal, inetrange, boolean, boolean) RETURNS internal AS 'range_agg', 'range_agg_transfn' LANGUAGE c IMMUTABLE; CREATE OR REPLACE FUNCTION range_agg_finalfn(internal, inetrange, boolean, boolean) RETURNS inetrange AS 'range_agg', 'range_agg_finalfn' LANGUAGE c IMMUTABLE; CREATE AGGREGATE range_agg(inetrange, boolean, boolean) ( stype = internal, sfunc = range_agg_transfn, finalfunc = range_agg_finalfn, finalfunc_extra );
inetrange with your own range type, of course.)
This package installs like any Postgres extension. First say:
make && sudo make install
You will need to have
pg_config in your path,
but normally that is already the case.
You can check with
Then in the database of your choice say:
CREATE EXTENSION range_agg;
- Add a function to find gaps (see below).
Paul A. Jungwirth firstname.lastname@example.org
This extension was inspired by a blog post about aggregating ranges by Matt Schinckel.
He talks about merging ranges (like we do here)
and a related problem---finding the gaps between them---which I think would be nice to support here too. (Watch this space for updates. :-)
I was impressed by his solution,
which is original as far as I know,
of using the
lead window function.
Copyright (c) 2018 Paul A. Jungwirth
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