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9.30. Statistics Information Functions
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9.30. Statistics Information Functions #

PostgreSQL provides a function to inspect complex statistics defined using the CREATE STATISTICS command.

9.30.1. Inspecting MCV Lists #

pg_mcv_list_items ( pg_mcv_list ) → setof record

pg_mcv_list_items returns a set of records describing all items stored in a multi-column MCV list. It returns the following columns:

Name Type Description

Name	Type	Description
`index`	`integer`	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

index

integer

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 type can be obtained only from the pg_statistic_ext_data.stxdmcv column.

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