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