pg_stats

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.

Table 1. pg_stats

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.