The mysql.column_stats table was introduced as part of the Engine-independent table statistics feature implemented in MariaDB 10.0.1.
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.
In MariaDB 10.4 and later, this table uses the Aria storage engine.
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 NULLs, 0.5 - half values are NULLs, 1 - all values are NULLs). |
|
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. | |
hist_type |
enum('SINGLE_PREC_HB', 'DOUBLE_PREC_HB') |
YES | NULL |
Histogram type. See the histogram_type system variable. | |
histogram |
varbinary(255) |
YES | NULL |
It is possible to manually update the table. See Manual updates to statistics tables for details.
© 2019 MariaDB
Licensed under the Creative Commons Attribution 3.0 Unported License and the GNU Free Documentation License.
https://mariadb.com/kb/en/mysqlcolumn_stats-table/