9.29. Statistics Information Functions
PostgreSQL
provides a function to inspect complex
statistics defined using the
CREATE STATISTICS
command.
9.29.1. Inspecting MCV Lists
pg_mcv_list_items
returns a list of all items
stored in a multi-column
MCV
list, and returns the
following columns:
| Name | Type | Description |
|---|---|---|
index
|
int
|
index of the item in the MCV list |
values
|
text[]
|
values stored in the MCV item |
nulls
|
boolean[]
|
flags identifying
NULL
values
|
frequency
|
double precision
|
frequency of this MCV item |
base_frequency
|
double precision
|
base frequency of this MCV item |
The
pg_mcv_list_items
function can be used like this:
SELECT m.* FROM pg_statistic_ext join pg_statistic_ext_data on (oid = stxoid),
pg_mcv_list_items(stxdmcv) m WHERE stxname = 'stts';
Values of the
pg_mcv_list
can be obtained only from the
pg_statistic_ext_data.stxdmcv
column.