pg_stats_ext_exprs — PostgreSQL system view

The PostgreSQL pg_stats_ext_exprs system view: full column reference (names, types, descriptions), catalog relationships and version support.

The Sev-1 Admin
The Sev-1 Admin  ·  5 min read

Summary

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 owns, and therefore it is safe to allow public read access to this view.

(Description quoted from the official PostgreSQL documentation.)

Columns

The pg_stats_ext_exprs system view exposes the following columns (names, types and descriptions are taken verbatim from the PostgreSQL documentation):

  • schemaname name references pg_namespace.nspname
    Name of schema containing table
  • tablename name references pg_class.relname
    Name of table the statistics object is defined on
  • tableid oid references pg_class.oid
    OID of table the statistics object is defined on
  • 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_id oid references pg_statistic_ext.oid
    OID of extended statistics object
  • statistics_owner name references pg_authid.rolname
    Owner of the extended statistics object
  • expr text
    Expression included in the extended statistics object
  • 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
  • null_frac float4
    Fraction of expression entries that are null
  • avg_width int4
    Average width in bytes of expression’s entries
  • n_distinct float4
    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 ANALYZE believes that the number of distinct values is likely to increase as the table grows; the positive form is used when the expression seems to have a fixed number of possible values.) For example, -1 indicates a unique expression in which the number of distinct values is the same as the number of rows.
  • most_common_vals anyarray
    A list of the most common values in the expression. (Null if no values seem to be more common than any others.)
  • most_common_freqs float4[]
    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 most_common_vals is.)
  • histogram_bounds anyarray
    A list of values that divide the expression’s values into groups of approximately equal population. The values in most_common_vals, if present, are omitted from this histogram calculation. (This expression is null if the expression data type does not have a < operator or if the most_common_vals list accounts for the entire population.)
  • correlation float4
    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 < operator.)
  • most_common_elems anyarray
    A list of non-null element values most often appearing within values of the expression. (Null for scalar types.)
  • most_common_elem_freqs float4[]
    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 per-element frequencies; these are the minimum and maximum of the preceding per-element frequencies, and optionally the frequency of null elements. (Null when most_common_elems is.)
  • elem_count_histogram float4[]
    A histogram of the counts of distinct non-null element values within the values of the expression, followed by the average number of distinct non-null elements. (Null for scalar types.)
  • range_length_histogram anyarray
    A histogram of the lengths of non-empty and non-null range values of an expression. (Null for non-range types.) This histogram is calculated using the subtype_diff range function regardless of whether range bounds are inclusive.
  • range_empty_frac float4
    Fraction of expression entries whose values are empty ranges. (Null for non-range types.)
  • range_bounds_histogram anyarray
    A histogram of lower and upper bounds of non-empty and non-null range values. (Null for non-range types.) These two histograms are represented as a single array of ranges, whose lower bounds represent the histogram of lower bounds, and upper bounds represent the histogram of upper bounds.

Related catalogs

This object references the following other system catalogs:

Version applicability

Present in PostgreSQL 17, 18, 19 (verified against each release’s documentation). This is a long-standing system object that also exists in earlier PostgreSQL releases.

Related & references

Reference: PostgreSQL documentation — pg_stats_ext_exprs.