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51.89. 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 catalogs
— 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 columns the extended statistics is defined on 
kinds  text[]  Types of extended statistics enabled for this record  
n_distinct  pg_ndistinct  Ndistinct counts for combinations of column values. 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 of values in the columns. (Null if no combinations 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.