Compute an aggregated tsrange from a set of entries? - sql

Question

I am trying to compute a aggregated tsrange from a set of row that I extract from an SQL query. Problem is that I keep getting errors that the input parameter is not being passed in.
CREATE OR REPLACE AGGREGATE range_merge(anyrange)
(
sfunc = range_merge,
stype = anyrange
);
DROP FUNCTION IF EXISTS aggregate_validity(entity_name regclass, entry bigint);
CREATE OR REPLACE FUNCTION aggregate_validity(entity_name regclass, entry bigint) returns tsrange AS
$$
DECLARE
result tsrange;
BEGIN
EXECUTE format('select range_merge(valid) from %s where entity_id = %U', entity_name, entry) into result;
return result;
END
$$ LANGUAGE plpgsql;
When I do:
select * from aggregate_validity(country, 1);
I get an error stating that the entity name and entry do not exist. It does not seem to parameterize the input into the statement properly.

Answer 1

Function:
EXECUTE format('select range_merge(valid) from %s where entity_id=%U',entity_name, entry)
into result;
=>
EXECUTE format('select range_merge(valid) from %I where entity_id=%s',entity_name, entry)
into result;
--%I for identifier, %s for value
Call:
select * from aggregate_validity(country, 1)
=>
select * from aggregate_validity('country', 1);
db<>fiddle demo

Answer 2

CREATE OR REPLACE AGGREGATE range_merge(anyrange) (
SFUNC = range_merge
, STYPE = anyrange
);
-- DROP FUNCTION IF EXISTS aggregate_validity(entity_name regclass, entry bigint);
CREATE OR REPLACE FUNCTION aggregate_validity(entity_name regclass, entry bigint, OUT result tsrange)
LANGUAGE plpgsql AS
$func$
BEGIN
EXECUTE 'SELECT range_merge(valid) FROM ' || entity_name || ' WHERE entity_id = $1'
INTO result
USING entry;
END
$func$;
Call:
SELECT aggregate_validity('country', 1);
db<>fiddle here
The call does not need SELECT * FROM, as the function returns a single value per definition.
I used an OUT parameter to simplify (OUT result tsrange). See:
Returning from a function with OUT parameter
Don't concatenate the entry value into the SQL string. Pass it as value with the USING clause. Cleaner, faster.
Since entity_name is passed as regclass, it's safe to simply concatenate (which is a bit cheaper). See:
Table name as a PostgreSQL function parameter
Plus, missing quotes and incorrect format specifiers, as Lukasz already provided.
Your custom aggregate function range_merge() has some caveats:
I wouldn't name it "range_merge", that being the name of the plain function range_merge(), too. While that's legal, it still invites confusing errors.
You are aware that the function range_merge() includes gaps between input ranges in the output range?
range_merge() returns NULL for any NULL input. So if your table has any NULL values in the column valid, the result is always NULL. I strongly suggest that any involved columns shall be defined as NOT NULL.
If you are at liberty to install additional modules, consider range_agg by Paul Jungwirth who is also here on Stackovflow. It provides the superior function range_agg() addressing some of the mentioned issues.
If you don't want to include gaps, consider the Postgres Wiki page on range aggregation.
I would probably not use aggregate_validity() at all. It obscures the nested functionality from the Postgres query planner and may lead so suboptimal query plans. Typically, you can replace it with a correlated or a LATERAL subquery, which can be planned and optimized by Postgres in context of the outer query. I appended a demo to the fiddle:
db<>fiddle here
Related:
What is the difference between LATERAL and a subquery in PostgreSQL?