---
title: "pg_statistic"
id: catalog-pg-statistic
pg_version: "20devel"
---

<a id="catalog-pg-statistic"></a>

## 52.56. pg_statistic

The catalog pg_statistic stores statistical data about the contents of the database. Entries are created by [`ANALYZE`](sql-analyze.md) 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 or partitions, 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 column FROM table*`, whereas the `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](view-pg-stats.md) is a publicly readable view on pg_statistic that only exposes information about those tables that are readable by the current user. 

**pg_statistic Columns**

| Column Type | Description | 
| --- | --- |
| `starelid` `oid` (references [pg_class](catalog-pg-class.md).`oid`) | The table or index that the described column belongs to |
| `staattnum` `int2` (references [pg_attribute](catalog-pg-attribute.md).`attnum`) | The number of the described column |
| `stainherit` `bool` | If true, the stats include values from child tables, 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`N`` `int2` | A code number indicating the kind of statistics stored in the `N`th "slot" of the pg_statistic row. |
| `staop`N`` `oid` (references [pg_operator](catalog-pg-operator.md).`oid`) | An operator used to derive the statistics stored in the `N`th "slot". For example, a histogram slot would show the `<` operator that defines the sort order of the data. Zero if the statistics kind does not require an operator. |
| `stacoll`N`` `oid` (references [pg_collation](catalog-pg-collation.md).`oid`) | The collation used to derive the statistics stored in the `N`th "slot". For example, a histogram slot for a collatable column would show the collation that defines the sort order of the data. Zero for noncollatable data. |
| `stanumbers`N`` `float4[]` | Numerical statistics of the appropriate kind for the `N`th "slot", or null if the slot kind does not involve numerical values |
| `stavalues`N`` `anyarray` | Column data values of the appropriate kind for the `N`th "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 than `anyarray`. |