mysql.column_stats Table

The mysql.column_stats table is one of three tables storing data used for Engine-independent table statistics added in MariaDB 10.0.1. The others are mysql.table_stats and mysql.index_stats.The histogram fields were added in MariaDB 10.0.2 as part of the Histogram-based Statistics feature.

Note that statistics for blob and text columns are not collected. If explicitly specified, a warning is returned.

MariaDB starting with 10.4

In MariaDB 10.4 and later, this table uses the Aria storage engine.

MariaDB until 10.3

In MariaDB 10.3 and before, this table uses the MyISAM storage engine.

The mysql.column_stats table contains the following fields:

Field	Type	Null	Key	Default	Description
`db_name`	`varchar(64)`	NO	PRI	`NULL`	Database the table is in.
`table_name`	`varchar(64)`	NO	PRI	`NULL`	Table name.
`column_name`	`varchar(64)`	NO	PRI	`NULL`	Name of the column.
`min_value`	`varchar(255)`	YES		`NULL`	Minimum value in the table (in text form).
`max_value`	`varchar(255)`	YES		`NULL`	Maximum value in the table (in text form).
`nulls_ratio`	`decimal(12,4)`	YES		`NULL`	Fraction of `NULL` values (0- no `NULL`s, 0.5 - half values are `NULL`s, 1 - all values are `NULL`s).
`avg_length`	`decimal(12,4)`	YES		`NULL`	Average length of column value, in bytes. Counted as if one ran `SELECT AVG(LENGTH(col))`. This doesn't count `NULL` bytes, assumes endspace removal for `CHAR(n)`, etc.
`avg_frequency`	`decimal(12,4)`	YES		`NULL`	Average number of records with the same value
`hist_size`	`tinyint(3) unsigned`	YES		`NULL`	Histogram size in bytes, from 0-255, or, from MariaDB 10.7, number of buckets if the histogram type is `JSON_HB`.
`hist_type`	`enum('SINGLE_PREC_HB', 'DOUBLE_PREC_HB')` (>= MariaDB 10.7) `enum('SINGLE_PREC_HB', 'DOUBLE_PREC_HB','JSON_HB')` (<= MariaDB 10.6)	YES		`NULL`	Histogram type. See the histogram_type system variable.
`histogram`	`blob` (>= MariaDB 10.7) `varbinary(255)` (<=MariaDB 10.6)	YES		`NULL`

It is possible to manually update the table. See Manual updates to statistics tables for details.

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https://mariadb.com/kb/en/mysqlcolumn_stats-table/