pg_stats
The pg_stats is a publicly readable view on pg_statistic that only exposes information about those tables that are readable by the current user. The pg_stats view presents the contents of pg_statistic in a friendlier format.
All the statistical data is inherently approximate, even assuming that it is up-to-date. The pg_stats schema must be extended whenever new slot types are defined.
| Name | Type | References | Description |
|---|---|---|---|
| schemaname | name | pg_namespace.nspname. | The name of the schema containing the table. |
| tablename | name | pg_class.relname | The name of the table. |
| attname | name | pg_attribute.attname | The name of the column this row describes. |
| null_frac | real | The fraction of column entries that are null. | |
| avg_width | integer | The average storage width in bytes of the column’s entries, calculated as avg(pg_column_size(column_name)). |
|
| n_distinct | real | A positive number is an estimate of the number of distinct values in the column; the number is not expected to vary with the number of rows. A negative value is the number of distinct values divided by the number of rows, that is, the ratio of rows with distinct values for the column, negated. This form is used when the number of distinct values increases with the number of rows. A unique column, for example, has an n_distinct value of -1.0. Columns with an average width greater than 1024 are considered unique. |
|
| most_common-vals | anyarray | An array containing the most common values in the column, or null if no values seem to be more common. If the n_distinct column is -1, most_common_vals is null. The length of the array is the lesser of the number of actual distinct column values or the value of the default_statistics_target configuration parameter. The number of values can be overridden for a column using ALTER TABLE table SET COLUMN column SET STATISTICS N. |
|
| most_common_freqs | real[] | An array containing the frequencies of the values in the most_common_vals array. This is the number of occurrences of the value divided by the total number of rows. The array is the same length as the most_common_vals array. It is null if most_common_vals is null. |
|
| histogram_bounds | anyarray | An array of values that divide the column values into groups of approximately the same size. A histogram can be defined only if there is a max() aggregate function for the column. The number of groups in the histogram is the same as the most_common_vals array size. |
|
| correlation | real | HAWQ does not calculate the correlation statistic. |