mysql.column_stats Table
The mysql.column_stats table is one of three tables storing data used for Engine-independent table statistics. The others are mysql.table_stats and mysql.index_stats.
It is populated when the ANALYZE TABLE statement is run, although not by default. See Collecting Statistics with the ANALYZE TABLE Statement for details.
Note that statistics for blob and text columns are not collected. If explicitly specified, a warning is returned.
It is possible to manually update the table and, unlike most system tables, there are some scenarios where this could be useful. See Manual updates to statistics tables for details.
This table uses the Aria 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, or, from MariaDB 10.8, number of buckets if the histogram type is JSON_HB. | |
hist_type | enum('SINGLE_PREC_HB', 'DOUBLE_PREC_HB') (>= MariaDB 10.8)enum('SINGLE_PREC_HB', 'DOUBLE_PREC_HB','JSON_HB') (<= MariaDB 10.7) | YES | NULL | Histogram type. See the histogram_type system variable. | |
histogram | blob (>= MariaDB 10.7)varbinary(255) (<=MariaDB 10.7) | YES | NULL |
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