版本：11
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.
pg_statistic_ext ColumnsColumn Type
Description
oid oid
Row identifier
stxrelid oid (references .oid)
Table containing the columns described by this object
stxname name
Name of the statistics object
stxnamespace oid (references .oid)
The OID of the namespace that contains this statistics object
stxowner oid (references .oid)
Owner of the statistics object
stxstattarget int4
stxstattarget controls the level of detail of statistics accumulated for this statistics object by . A zero value indicates that no statistics should be collected. A negative 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.
stxkeys int2vector (references .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
stxkind char[]
An array containing codes for the enabled statistic kinds; valid values are: d for n-distinct statistics, f for functional dependency statistics, and m for most common values (MCV) list statistics
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.