rollup()

Toolkit

TimescaleDB Toolkit functions are available under Timescale Community Edition. They are automatically included with Timescale Cloud. Click to learn more.

rollup(
    log hyperloglog
) RETURNS Hyperloglog

Returns a hyperloglog by aggregating over the union of the input elements. Since hyperloglog is designed to merge well, rollup does not compound errors. Union of hyperloglogs of different bucket size is currently not supported.

For more information about approximate count distinct functions, see the hyperfunctions documentation.

Required arguments

Returns

Sample usage

SELECT distinct_count(rollup(logs))
FROM (
    (SELECT hyperloglog(32768, v::text) logs FROM generate_series(1, 100000) v)
    UNION ALL
    (SELECT hyperloglog(32768, v::text) FROM generate_series(50000, 150000) v)
) hll;

 distinct_count 
----------------
         150147