mysql.column_stats Table
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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.
The 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. | |
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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