# 51.50. pg\_statistic 系統目錄 pg\_statistic 儲存有關資料庫內容的統計數據。內容項目是由 [ANALYZE](/12/reference/sql-commands/analyze.md) 所建立的，隨後由查詢計劃程序使用。請注意，所有統計數據本質上都是趨近的，即使假設上它是最新的數據。 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` *`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`](https://www.postgresql.org/docs/10/static/view-pg-stats.html) is a publicly readable view on `pg_statistic` that only exposes information about those tables that are readable by the current user. ## **Table 51.50. `pg_statistic` Columns** | Name | Type | References | Description | | ----------------- | ---------- | -------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | `starelid` | `oid` | [`pg_class`](https://www.postgresql.org/docs/10/static/catalog-pg-class.html).oid | The table or index that the described column belongs to | | `staattnum` | `int2` | [`pg_attribute`](https://www.postgresql.org/docs/10/static/catalog-pg-attribute.html).attnum | 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`*`N`* | `int2` | | A code number indicating the kind of statistics stored in the \_`N`\_th “slot” of the `pg_statistic` row. | | `staop`*`N`* | `oid` | [`pg_operator`](https://www.postgresql.org/docs/10/static/catalog-pg-operator.html).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. | | `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`. | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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