mysql.column_stats Table

MariaDB starting with 10.0.1

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.

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 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.

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