PG_EXT_STATS

PG_EXT_STATS allows for access to extension statistics stored in the PG_STATISTIC_EXT system catalog. Currently, the extended statistics include the multi-column statistics. The current feature is a lab feature. Contact Huawei technical support before using it.

**Table 1** PG_EXT_STATS columns
Name	Type	Reference	Description
schemaname	name	PG_NAMESPACE.nspname	Name of the schema that contains a table
tablename	name	PG_CLASS.relname	Table name
attname	int2vector	PG_STATISTIC_EXT.stakey	Columns to be combined for collecting statistics
inherited	boolean	-	Includes inherited sub-columns if the value is true; otherwise, it indicates the column in a specified table.
null_frac	real	-	Percentage of column combinations that are null to all records
avg_width	integer	-	Average width of column combinations, in byte
n_distinct	real	-	Estimated number of distinct values in a column combination if the value is greater than 0 Negative of the number of distinct values divided by the number of rows if the value is less than 0 The negated form is used when ANALYZE believes that the number of distinct values is likely to increase as the table grows. The positive form is used when the column seems to have a fixed number of possible values. For example, –1 indicates that the number of distinct values is the same as the number of rows for a column combination. The number of distinct values is unknown if the value is 0.
n_dndistinct	real	-	Number of unique not-null data values in the dn1 column combination Exact number of distinct values if the value is greater than 0. Negative of the number of distinct values divided by the number of rows if the value is less than 0 For example, if a value in a column combination appears twice in average, n_dndistinct equals –0.5. The number of distinct values is unknown if the value is 0.
most_common_vals	anyarray	-	List of the most common values in a column combination. If this combination does not have the most common values, most_common_vals will be NULL. None of the most common values in most_common_vals is NULL.
most_common_freqs	real[]	-	List of the frequencies of the most common values, that is, the number of occurrences of each value divided by the total number of rows (NULL if most_common_vals is NULL)
most_common_vals_null	anyarray	-	List of the most common values in a column combination. If this combination does not have the most common values, most_common_vals will be NULL. At least one of the common values in most_common_vals_null is NULL.
most_common_freqs_null	real[]	-	List of the frequencies of the most common values, that is, the number of occurrences of each value divided by the total number of rows (NULL if most_common_vals_null is NULL)
histogram_bounds	anyarray	-	Boundary value list of the histogram