pg_stats_ext
The view pg_stats_ext
provides access to the information stored in the pg_statistic_ext
and pg_statistic_ext_data
catalogs. This view allows access only to rows of pg_statistic_ext
and pg_statistic_ext_data
that correspond to tables the user has permission to read, and therefore it is safe to allow public read access to this view.
pg_stats_ext
is also designed to present the information in a more readable format than the underlying catalog — at the cost that its schema must be extended whenever new types of extended statistics are added to pg_statistic_ext
.
Table 51.90. pg_stats_ext
Columns
Name  Type  References  Description 

schemaname 
name 

Name of schema containing table 
tablename 
name 

Name of table 
statistics_schemaname 
name 

Name of schema containing extended statistic 
statistics_name 
name 

Name of extended statistics 
statistics_owner 
oid 

Owner of the extended statistics 
attnames 
name[] 

Names of the column the extended statistics is defined on 
kinds 
text[] 
Types of exdended statistics enabled for this record  
n_distinct 
pg_ndistinct 
Ndistinct counts for combinations of columns. If greater than zero, the estimated number of distinct values in the combination. If less than zero, the negative of the number of distinct values divided by the number of rows. (The negated form is used when ANALYZE believes that the number of distinct values is likely to increase as the table grows; the positive form is used when the column seems to have a fixed number of possible values.) For example, 1 indicates a unique combination of columns in which the number of distinct combinations is the same as the number of rows. 

dependencies 
pg_dependencies 
Functional dependency statistics  
most_common_vals 
anyarray 
A list of the most common combinations in the columns. (Null if no values seem to be more common than any others.)  
most_common_val_nulls 
anyarray 
A list of NULL flags for the most common combinations of values. (Null when most_common_vals is.) 

most_common_freqs 
real[] 
A list of the frequencies of the most common combinations, i.e., number of occurrences of each divided by total number of rows. (Null when most_common_vals is.) 

most_common_base_freqs 
real[] 
A list of the base frequencies of the most common combinations, i.e., product of pervalue frequencies. (Null when most_common_vals is.) 
The maximum number of entries in the array fields can be controlled on a columnbycolumn basis using the ALTER TABLE SET STATISTICS
command, or globally by setting the default_statistics_target runtime parameter.