• MySQL 5.1 Reference Manual :: 20 INFORMATION_SCHEMA Tables :: 20.19 The INFORMATION_SCHEMA PARTITIONS Table
  • 20.19. The INFORMATION_SCHEMA PARTITIONS Table

    The PARTITIONS table provides information about table partitions. See Chapter 18, Partitioning, for more information about partitioning tables.

    INFORMATION_SCHEMA Name SHOW Name Remarks
    TABLE_CATALOG   MySQL extension
    TABLE_SCHEMA   MySQL extension
    TABLE_NAME   MySQL extension
    PARTITION_NAME   MySQL extension
    SUBPARTITION_NAME   MySQL extension
    PARTITION_ORDINAL_POSITION   MySQL extension
    SUBPARTITION_ORDINAL_POSITION   MySQL extension
    PARTITION_METHOD   MySQL extension
    SUBPARTITION_METHOD   MySQL extension
    PARTITION_EXPRESSION   MySQL extension
    SUBPARTITION_EXPRESSION   MySQL extension
    PARTITION_DESCRIPTION   MySQL extension
    TABLE_ROWS   MySQL extension
    AVG_ROW_LENGTH   MySQL extension
    DATA_LENGTH   MySQL extension
    MAX_DATA_LENGTH   MySQL extension
    INDEX_LENGTH   MySQL extension
    DATA_FREE   MySQL extension
    CREATE_TIME   MySQL extension
    UPDATE_TIME   MySQL extension
    CHECK_TIME   MySQL extension
    CHECKSUM   MySQL extension
    PARTITION_COMMENT   MySQL extension
    NODEGROUP   MySQL extension
    TABLESPACE_NAME   MySQL extension

    Notes:

    • The PARTITIONS table is a nonstandard table. It was added in MySQL 5.1.6.

      Each record in this table corresponds to an individual partition or subpartition of a partitioned table.

    • TABLE_CATALOG: This column is always NULL.

    • TABLE_SCHEMA: This column contains the name of the database to which the table belongs.

    • TABLE_NAME: This column contains the name of the table containing the partition.

    • PARTITION_NAME: The name of the partition.

    • SUBPARTITION_NAME: If the PARTITIONS table record represents a subpartition, then this column contains the name of subpartition; otherwise it is NULL.

    • PARTITION_ORDINAL_POSITION: All partitions are indexed in the same order as they are defined, with 1 being the number assigned to the first partition. The indexing can change as partitions are added, dropped, and reorganized; the number shown is this column reflects the current order, taking into account any indexing changes.

    • SUBPARTITION_ORDINAL_POSITION: Subpartitions within a given partition are also indexed and reindexed in the same manner as partitions are indexed within a table.

    • PARTITION_METHOD: One of the values RANGE, LIST, HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available partitioning types as discussed in Section 18.2, “Partition Types”.

    • SUBPARTITION_METHOD: One of the values HASH, LINEAR HASH, KEY, or LINEAR KEY; that is, one of the available subpartitioning types as discussed in Section 18.2.5, “Subpartitioning”.

    • PARTITION_EXPRESSION: This is the expression for the partitioning function used in the CREATE TABLE or ALTER TABLE statement that created the table's current partitioning scheme.

      For example, consider a partitioned table created in the test database using this statement:

      CREATE TABLE tp (
          c1 INT,
          c2 INT,
          c3 VARCHAR(25)
      )
      PARTITION BY HASH(c1 + c2)
      PARTITIONS 4;
      

      The PARTITION_EXPRESSION column in a PARTITIONS table record for a partition from this table displays c1 + c2, as shown here:

      mysql> SELECT DISTINCT PARTITION_EXPRESSION
           >     FROM INFORMATION_SCHEMA.PARTITIONS
           >     WHERE TABLE_NAME='tp' AND TABLE_SCHEMA='test';
      +----------------------+
      | PARTITION_EXPRESSION |
      +----------------------+
      | c1 + c2              |
      +----------------------+
      1 row in set (0.09 sec)
      
    • SUBPARTITION_EXPRESSION: This works in the same fashion for the subpartitioning expression that defines the subpartitioning for a table as PARTITION_EXPRESSION does for the partitioning expression used to define a table's partitioning.

      If the table has no subpartitions, then this column is NULL.

    • PARTITION_DESCRIPTION: This column is used for RANGE and LIST partitions. For a RANGE partition, it contains the value set in the partition's VALUES LESS THAN clause, which can be either an integer or MAXVALUE. For a LIST partition, this column contains the values defined in the partition's VALUES IN clause, which is a comma-separated list of integer values.

      For partitions whose PARTITION_METHOD is other than RANGE or LIST, this column is always NULL.

    • TABLE_ROWS: The number of table rows in the partition.

      For partitioned InnoDB tables, the row count given in the TABLE_ROWS column is only an estimated value used in SQL optimization, and may not always be exact.

    • AVG_ROW_LENGTH: The average length of the rows stored in this partition or subpartition, in bytes.

      This is the same as DATA_LENGTH divided by TABLE_ROWS.

    • DATA_LENGTH: The total length of all rows stored in this partition or subpartition, in bytes—that is, the total number of bytes stored in the partition or subpartition.

    • MAX_DATA_LENGTH: The maximum number of bytes that can be stored in this partition or subpartition.

    • INDEX_LENGTH: The length of the index file for this partition or subpartition, in bytes.

    • DATA_FREE: The number of bytes allocated to the partition or subpartition but not used.

    • CREATE_TIME: The time of the partition's or subpartition's creation.

    • UPDATE_TIME: The time that the partition or subpartition was last modified.

    • CHECK_TIME: The last time that the table to which this partition or subpartition belongs was checked.

      Note

      Some storage engines do not update this time; for tables using these storage engines, this value is always NULL.

    • CHECKSUM: The checksum value, if any; otherwise, this column is NULL.

    • PARTITION_COMMENT: This column contains the text of any comment made for the partition.

      The default value for this column is an empty string.

    • NODEGROUP: This is the nodegroup to which the partition belongs. This is relevant only to MySQL Cluster tables; otherwise the value of this column is always 0.

    • TABLESPACE_NAME: This column contains the name of the tablespace to which the partition belongs. Currently, the value of this column is always DEFAULT.

    • Important

      If any partitioned tables created in a MySQL version prior to MySQL 5.1.6 are present following an upgrade to MySQL 5.1.6 or later, it is not possible to SELECT from, SHOW, or DESCRIBE the PARTITIONS table. See Section C.1.48, “Changes in MySQL 5.1.6 (01 February 2006)” before upgrading from MySQL 5.1.5 or earlier to MySQL 5.1.6 or later.

    • A nonpartitioned table has one record in INFORMATION_SCHEMA.PARTITIONS; however, the values of the PARTITION_NAME, SUBPARTITION_NAME, PARTITION_ORDINAL_POSITION, SUBPARTITION_ORDINAL_POSITION, PARTITION_METHOD, SUBPARTITION_METHOD, PARTITION_EXPRESSION, SUBPARTITION_EXPRESSION, and PARTITION_DESCRIPTION columns are all NULL. (The PARTITION_COMMENT column in this case is blank.)

      In MySQL 5.1, there is also only one record in the PARTITIONS table for a table using the NDBCLUSTER storage engine. The same columns are also NULL (or empty) as for a nonpartitioned table.