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`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 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 `

, 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 51.51. pg_statistic Columns**

Column Type Description |
---|

The table or index that the described column belongs to |

The number of the described column |

If true, the stats include values from child tables, not just the values in the specified relation |

The fraction of the column's entries that are null |

The average stored width, in bytes, of nonnull entries |

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 |

A code number indicating the kind of statistics stored in the `pg_statistic` row. |

An operator used to derive the statistics stored in the `<` operator that defines the sort order of the data. Zero if the statistics kind does not require an operator. |

The collation used to derive the statistics stored in the |

Numerical statistics of the appropriate kind for the |

Column data values of the appropriate kind for the `anyarray` . |

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