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The view pg_stats_ext provides access to information about each extended statistics object in the database, combining 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 owns, 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 53.31. pg_stats_ext Columns
Column Type
Description
schemaname name (references pg_namespace.nspname)
Name of schema containing table
tablename name (references pg_class.relname)
Name of table
statistics_schemaname name (references pg_namespace.nspname)
Name of schema containing extended statistics object
statistics_name name (references pg_statistic_ext.stxname)
Name of extended statistics object
statistics_owner name (references pg_authid.rolname)
Owner of the extended statistics object
attnames name[] (references pg_attribute.attname)
Names of the columns included in the extended statistics object
exprs text[]
Expressions included in the extended statistics object
kinds char[]
Types of extended statistics object enabled for this record
inherited bool (references pg_statistic_ext_data.stxdinherit)
If true, the stats include values from child tables, not just the values in the specified relation
n_distinct pg_ndistinct
N-distinct 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 text[]
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 bool[]
A list of NULL flags for the most common combinations of values. (Null when most_common_vals is.)
most_common_freqs float8[]
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 float8[]
A list of the base frequencies of the most common combinations, i.e., product of per-value frequencies. (Null when most_common_vals is.)
The maximum number of entries in the array fields can be controlled on a column-by-column basis using the ALTER TABLE SET STATISTICS command, or globally by setting the default_statistics_target run-time parameter.
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