52.91. pg_stats_ext_exprs
The view
pg_stats_ext_exprs
provides access to
information about all expressions included in extended statistics objects,
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 has permission to read, and therefore
it is safe to allow public read access to this view.
pg_stats_ext_exprs
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 the structure
of statistics in
pg_statistic_ext
changes.
Table 52.92.
pg_stats_ext_exprs
Columns
Column Type Description 

Name of schema containing table 
Name of table the statistics object is defined on 
Name of schema containing extended statistics object 
Name of extended statistics object 
Owner of the extended statistics object 
Expression included in the extended statistics object 
Fraction of expression entries that are null 
Average width in bytes of expression's entries 
If greater than zero, the estimated number of distinct values in the
expression. If less than zero, the negative of the number of distinct
values divided by the number of rows. (The negated form is used when

A list of the most common values in the expression. (Null if no values seem to be more common than any others.) 
A list of the frequencies of the most common values,
i.e., number of occurrences of each divided by total number of rows.
(Null when

A list of values that divide the expression's values into groups of
approximately equal population. The values in

Statistical correlation between physical row ordering and
logical ordering of the expression values. This ranges from 1 to +1.
When the value is near 1 or +1, an index scan on the expression will
be estimated to be cheaper than when it is near zero, due to reduction
of random access to the disk. (This expression is null if the expression's
data type does not have a

A list of nonnull element values most often appearing within values of the expression. (Null for scalar types.) 
A list of the frequencies of the most common element values, i.e., the
fraction of rows containing at least one instance of the given value.
Two or three additional values follow the perelement frequencies;
these are the minimum and maximum of the preceding perelement
frequencies, and optionally the frequency of null elements.
(Null when

A histogram of the counts of distinct nonnull element values within the values of the expression, followed by the average number of distinct nonnull elements. (Null for scalar types.) 
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.