PG_STATISTIC_EXT

PG_STATISTIC_EXT records extended statistics of tables in a database, such as statistics of multiple columns. Statistics of expressions will be supported later. You can specify the extended statistics to collect. This system catalog is accessible only to system administrators.

Table 1 PG_STATISTIC_EXT columns

Name	Type	Description
starelid	oid	Table or index that the described column belongs to
starelkind	"char"	Type of an object
stainherit	Boolean	Whether to collect statistics for objects that have inheritance relationship
stanullfrac	real	Percentage of column entries that are null
stawidth	integer	Average stored width, in bytes, of non-null entries
stadistinct	real	Number of distinct, non-NULL data values in the column for database nodes A value greater than 0 is the actual number of distinct values. A value less than 0 is the negative of a multiplier for the number of rows in the table. (For example, stadistinct=-0.5 indicates that values in a column appear twice on average.) The value 0 indicates that the number of distinct values is unknown.
stadndistinct	real	Number of unique non-null data values in the dn1 column A value greater than 0 is the actual number of distinct values. A value less than 0 is the negative of a multiplier for the number of rows in the table. (For example, stadistinct=-0.5 indicates that values in a column appear twice on average.) The value 0 indicates that the number of distinct values is unknown.
stakindN	smallint	Code number stating that the type of statistics is stored in slot N of the pg_statistic row Value range: 1 to 5
staopN	oid	Operator used to generate the statistics stored in slot N. For example, a histogram slot shows the < operator that defines the sort order of the data. Value range: 1 to 5
stakey	int2vector	Array of a column ID
stanumbersN	real[]	Numerical statistics of the appropriate type for slot N. The value is NULL if the slot does not involve numerical values. Value range: 1 to 5
stavaluesN	anyarray	Column data values of the appropriate type for slot N. The value is NULL if the slot type does not store any data values. Each array's element values are actually of the specific column's data type so there is no way to define these columns' type more specifically than anyarray. Value range: 1 to 5
staexprs	pg_node_tree	Expression corresponding to the extended statistics information.