PostgreSQL 如果想知道表中某个条件查询条件在索引中效率 ？

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dvdrental=# \d pg_stats
                     View "pg_catalog.pg_stats"
         Column         |   Type   | Collation | Nullable | Default 
------------------------+----------+-----------+----------+---------
 schemaname             | name     |           |          | 
 tablename              | name     |           |          | 
 attname                | name     |           |          | 
 inherited              | boolean  |           |          | 
 null_frac              | real     |           |          | 
 avg_width              | integer  |           |          | 
 n_distinct             | real     |           |          | 
 most_common_vals       | anyarray |           |          | 
 most_common_freqs      | real[]   |           |          | 
 histogram_bounds       | anyarray |           |          | 
 correlation            | real     |           |          | 
 most_common_elems      | anyarray |           |          | 
 most_common_elem_freqs | real[]   |           |          | 
 elem_count_histogram   | real[]   |           |          | 

dvdrental=# select *,t_vals.freqs::float * t_rels.reltuples as rows 
from (SELECT tablename,attname,unnest(most_common_vals::text::text[]) as vals,unnest(most_common_freqs::text::float[]) as freqs FROM pg_stats) as t_vals
left join (SELECT relname,reltuples FROM g_class CLS LEFT JOIN pg_namespace N ON ( N.oid = CLS.relnamespace ) 
            WHERE nspname NOT IN ( 'pg_catalog', 'information_schema' ) AND relkind = 'r') as t_rels on t_vals.tablename = t_rels.relname 
            where t_rels.relname in ('actor')
dvdrental-# ;
 tablename |   attname   |          vals          | freqs | relname | reltuples | rows 
-----------+-------------+------------------------+-------+---------+-----------+------
 actor     | first_name  | Austin                 |  0.02 | actor   |       200 |    4
 actor     | first_name  | Kenneth                |  0.02 | actor   |       200 |    4
 actor     | first_name  | Penelope               |  0.02 | actor   |       200 |    4
 actor     | first_name  | Burt                   | 0.015 | actor   |       200 |    3
 actor     | first_name  | Cameron                | 0.015 | actor   |       200 |    3
 actor     | first_name  | Christian              | 0.015 | actor   |       200 |    3
 actor     | first_name  | Cuba                   | 0.015 | actor   |       200 |    3
 actor     | first_name  | Dan                    | 0.015 | actor   |       200 |    3
 actor     | first_name  | Ed                     | 0.015 | actor   |       200 |    3
 actor     | first_name  | Fay                    | 0.015 | actor   |       200 |    3
 actor     | first_name  | Gene                   | 0.015 | actor   |       200 |    3

with first_name as (
select *,t_vals.freqs::float as freqs_1 
from (SELECT tablename,attname,
unnest(most_common_vals::text::text[]) as vals,
unnest(most_common_freqs::text::float[]) as freqs FROM pg_stats) as t_vals
left join (SELECT relname,reltuples FROM pg_class CLS 
           LEFT JOIN pg_namespace N ON ( N.oid = CLS.relnamespace ) 
           WHERE nspname NOT IN ( 'pg_catalog', 'information_schema' ) AND relkind = 'r') as t_rels on t_vals.tablename = t_rels.relname 
           where t_rels.relname in ('actor') and attname = 'first_name'),
last_name as (
select *,t_vals.freqs::float as freqs_2
from (SELECT tablename,attname,
      unnest(most_common_vals::text::text[]) as vals,
   unnest(most_common_freqs::text::float[]) as freqs FROM pg_stats) as t_vals
left join (SELECT relname,reltuples FROM pg_class CLS 
           LEFT JOIN pg_namespace N ON ( N.oid = CLS.relnamespace ) 
           WHERE nspname NOT IN ( 'pg_catalog', 'information_schema' ) AND relkind = 'r') as t_rels on t_vals.tablename = t_rels.relname 
           where t_rels.relname in ('actor') and attname = 'first_name')   
select first_name.attname as first_name,last_name.attname as last_name,
first_name.vals,last_name.vals,first_name.freqs_1,last_name.freqs_2,first_name.freqs_1 * last_name.freqs_2 as index_qua
from first_name 
left join  last_name on first_name.tablename = last_name.tablename
order by index_qua desc;