9.31. Statistics Information Functions
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## 9.31. Statistics Information Functions #

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

### 9.31.1. 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
--- | --- | ---
`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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