52.52. `pg_statistic_ext`
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## 52.52. `pg_statistic_ext` #

The catalog `pg_statistic_ext` holds definitions of extended planner statistics. Each row in this catalog corresponds to a statistics object created with `CREATE STATISTICS`.

Table 52.52. `pg_statistic_ext` Columns

Column Type Description
`oid` `oid` Row identifier
`stxrelid` `oid` (references `pg_class`.`oid`) Table containing the columns described by this object
`stxname` `name` Name of the statistics object
`stxnamespace` `oid` (references `pg_namespace`.`oid`) The OID of the namespace that contains this statistics object
`stxowner` `oid` (references `pg_authid`.`oid`) Owner of the statistics object
`stxkeys` `int2vector` (references `pg_attribute`.`attnum`) An array of attribute numbers, indicating which table columns are covered by this statistics object; for example a value of `1 3` would mean that the first and the third table columns are covered

`stxstattarget` `int2`

`stxstattarget` controls the level of detail of statistics accumulated for this statistics object by `ANALYZE`. A zero value indicates that no statistics should be collected. A null value says to use the maximum of the statistics targets of the referenced columns, if set, or the system default statistics target. Positive values of `stxstattarget` determine the target number of “most common values” to collect.

`stxkind` `char[]` An array containing codes for the enabled statistics kinds; valid values are: `d` for n-distinct statistics, `f` for functional dependency statistics, `m` for most common values (MCV) list statistics, and `e` for expression statistics
`stxexprs` `pg_node_tree` Expression trees (in `nodeToString()` representation) for statistics object attributes that are not simple column references. This is a list with one element per expression. Null if all statistics object attributes are simple references.

The `pg_statistic_ext` entry is filled in completely during `CREATE STATISTICS`, but the actual statistical values are not computed then. Subsequent `ANALYZE` commands compute the desired values and populate an entry in the `pg_statistic_ext_data` catalog.

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