18.3 Partition Management

18.3.1 Management of RANGE and LIST Partitions
18.3.2 Management of HASH and KEY Partitions
18.3.3 Maintenance of Partitions
18.3.4 Obtaining Information About Partitions

MySQL 5.1 provides a number of ways to modify partitioned tables. It is possible to add, drop, redefine, merge, or split existing partitions. All of these actions can be carried out using the partitioning extensions to the ALTER TABLE statement Section 13.1.7, “ALTER TABLE Syntax”. There are also ways to obtain information about partitioned tables and partitions. We discuss these topics in the sections that follow.

Note

In MySQL 5.1, all partitions of a partitioned table must have the same number of subpartitions, and it is not possible to change the subpartitioning once the table has been created.

The statement ALTER TABLE ... PARTITION BY ... is available and is functional beginning with MySQL 5.1.6; previously in MySQL 5.1, this was accepted as valid syntax, but the statement did nothing.

To change a table's partitioning scheme, it is necessary only to use the ALTER TABLE statement with a partition_options clause. This clause has the same syntax as that as used with CREATE TABLE for creating a partitioned table, and always begins with the keywords PARTITION BY. Suppose that you have a table partitioned by range using the following CREATE TABLE statement:

CREATE TABLE trb3 (id INT, name VARCHAR(50), purchased DATE)
    PARTITION BY RANGE( YEAR(purchased) ) (
        PARTITION p0 VALUES LESS THAN (1990),
        PARTITION p1 VALUES LESS THAN (1995),
        PARTITION p2 VALUES LESS THAN (2000),
        PARTITION p3 VALUES LESS THAN (2005)
    );

To repartition this table so that it is partitioned by key into two partitions using the id column value as the basis for the key, you can use this statement:

ALTER TABLE trb3 PARTITION BY KEY(id) PARTITIONS 2;

This has the same effect on the structure of the table as dropping the table and re-creating it using CREATE TABLE trb3 PARTITION BY KEY(id) PARTITIONS 2;.

In MySQL 5.1.7 and earlier MySQL 5.1 releases, ALTER TABLE ... ENGINE = ... removed all partitioning from the affected table. Beginning with MySQL 5.1.8, this statement changes only the storage engine used by the table, and leaves the table's partitioning scheme intact. As of MySQL 5.1.8, use ALTER TABLE ... REMOVE PARTITIONING to remove a table's partitioning. See Section 13.1.7, “ALTER TABLE Syntax”.

Important

Only a single PARTITION BY, ADD PARTITION, DROP PARTITION, REORGANIZE PARTITION, or COALESCE PARTITION clause can be used in a given ALTER TABLE statement. If you (for example) wish to drop a partition and reorganize a table's remaining partitions, you must do so in two separate ALTER TABLE statements (one using DROP PARTITION and then a second one using REORGANIZE PARTITIONS).