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 command (see Section 13.1.2, “ALTER TABLE Syntax”, for syntax definitions). 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 command 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. For example, 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;.