9.29. Statistics Information Functions

PostgreSQL provides a function to inspect complex statistics defined using the CREATE STATISTICS command.

9.29.1. Inspecting MCV Lists

pg_mcv_list_items returns a list of all items stored in a multi-column MCV list, and returns the following columns:

Name Type Description
index int index of the item in the MCV list
values text[] values stored in the MCV item
nulls boolean[] flags identifying NULL values
frequency double precision frequency of this MCV item
base_frequency double precision base frequency of this MCV item

The pg_mcv_list_items function can be used like this:

SELECT m.* FROM pg_statistic_ext join pg_statistic_ext_data on (oid = stxoid),
                pg_mcv_list_items(stxdmcv) m WHERE stxname = 'stts';

Values of the pg_mcv_list can be obtained only from the pg_statistic_ext_data.stxdmcv column.