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