num_vals()

URL: llms-txt#num_vals()

===== PAGE: https://docs.tigerdata.com/api/_hyperfunctions/uddsketch/intro/ =====

Estimate the value at a given percentile, or the percentile rank of a given value, using the UddSketch algorithm. This estimation is more memory- and CPU-efficient than an exact calculation using Postgres's percentile_cont and percentile_disc functions.

uddsketch is one of two advanced percentile approximation aggregates provided in TimescaleDB Toolkit. It produces stable estimates within a guaranteed relative error.

The other advanced percentile approximation aggregate is [tdigest][tdigest], which is more accurate at extreme quantiles, but is somewhat dependent on input order.

If you aren't sure which aggregate to use, try the default percentile estimation method, [percentile_agg][percentile_agg]. It uses the uddsketch algorithm with some sensible defaults.

For more information about percentile approximation algorithms, see the [algorithms overview][algorithms].

===== PAGE: https://docs.tigerdata.com/api/_hyperfunctions/uddsketch/approx_percentile_rank/ =====