pg_statistic
   The catalog pg_statistic stores
   statistical data about the contents of the database.  Entries are
   created by ANALYZE
   and subsequently used by the query planner.  Note that all the
   statistical data is inherently approximate, even assuming that it
   is up-to-date.
  
   Normally there is one entry, with stainherit =
   false, for each table column that has been analyzed.
   If the table has inheritance children, a second entry with
   stainherit = true is also created.  This row
   represents the column's statistics over the inheritance tree, i.e.,
   statistics for the data you'd see with
   SELECT ,
   whereas the column FROM table*stainherit = false row represents
   the results of
   SELECT .
  column FROM ONLY table
   pg_statistic also stores statistical data about
   the values of index expressions.  These are described as if they were
   actual data columns; in particular, starelid
   references the index.  No entry is made for an ordinary non-expression
   index column, however, since it would be redundant with the entry
   for the underlying table column.  Currently, entries for index expressions
   always have stainherit = false.
  
   Since different kinds of statistics might be appropriate for different
   kinds of data, pg_statistic is designed not
   to assume very much about what sort of statistics it stores.  Only
   extremely general statistics (such as nullness) are given dedicated
   columns in pg_statistic.  Everything else
   is stored in “slots”, which are groups of associated columns
   whose content is identified by a code number in one of the slot's columns.
   For more information see
   src/include/catalog/pg_statistic.h.
  
   pg_statistic should not be readable by the
   public, since even statistical information about a table's contents
   might be considered sensitive.  (Example: minimum and maximum values
   of a salary column might be quite interesting.)
   pg_stats
   is a publicly readable view on
   pg_statistic that only exposes information
   about those tables that are readable by the current user.
  
Table 52.50. pg_statistic Columns
| Name | Type | References | Description | 
|---|---|---|---|
| starelid | oid |  | The table or index that the described column belongs to | 
| staattnum | int2 |  | The number of the described column | 
| stainherit | bool | If true, the stats include inheritance child columns, not just the values in the specified relation | |
| stanullfrac | float4 | The fraction of the column's entries that are null | |
| stawidth | int4 | The average stored width, in bytes, of nonnull entries | |
| stadistinct | float4 | The number of distinct nonnull data values in the column.
      A value greater than zero is the actual number of distinct values.
      A value less than zero is the negative of a multiplier for the number
      of rows in the table; for example, a column in which about 80% of the
      values are nonnull and each nonnull value appears about twice on
      average could be represented by stadistinct= -0.4.
      A zero value means the number of distinct values is unknown. | |
| stakind | int2 | A code number indicating the kind of statistics stored in the Nth “slot” of thepg_statisticrow. | |
| staop | oid |  | An operator used to derive the statistics stored in the Nth “slot”.  For example, a
       histogram slot would show the<operator
       that defines the sort order of the data. | 
| stanumbers | float4[] | Numerical statistics of the appropriate kind for the Nth “slot”, or null if the slot
       kind does not involve numerical values | |
| stavalues | anyarray | Column data values of the appropriate kind for the Nth “slot”, or null if the slot
       kind does not store any data values.  Each array's element
       values are actually of the specific column's data type, or a related
       type such as an array's element type, so there is no way to define
       these columns' type more specifically thananyarray. |