49.89. 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 49.90. 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 | 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 | 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 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.