9.30. Statistics Information Functions #
PostgreSQL provides a function to inspect complex statistics defined using the CREATE STATISTICS command.
9.30.1. Inspecting MCV Lists #
pg_mcv_list_items(pg_mcv_list) →setof record
pg_mcv_list_items returns a set of records describing all items stored in a multi-column MCV list. It returns the following columns:
| Name | Type | Description |
|---|---|---|
index | integer | 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 type can be obtained only from the pg_statistic_ext_data.stxdmcv column.