MySQL :: MySQL 5.1 Reference Manual :: 13.1.7.1 ALTER TABLE Partition Operations

MySQL :: MySQL 5.1 Reference Manual :: 13.1.7.1 ALTER TABLE Partition Operations:

• Simply using a partition_options clause with ALTER TABLE on a partitioned table repartitions the table according to the partitioning scheme defined by the partition_options. This clause always begins withPARTITION BY, and follows the same syntax and other rules as apply to the partition_options clause forCREATE TABLE (see Section 13.1.17, “CREATE TABLE Syntax”, for more detailed information), and can also be used to partition an existing table that is not already partitioned. For example, consider a (nonpartitioned) table defined as shown here:

  CREATE TABLE t1 (
      id INT,
      year_col INT
  );

  This table can be partitioned by HASH, using the id column as the partitioning key, into 8 partitions by means of this statement:

  ALTER TABLE t1
      PARTITION BY HASH(id)
      PARTITIONS 8;

  The table that results from using an ALTER TABLE ... PARTITION BY statement must follow the same rules as one created using CREATE TABLE ... PARTITION BY. This includes the rules governing the relationship between any unique keys (including any primary key) that the table might have, and the column or columns used in the partitioning expression, as discussed in Section 18.5.1, “Partitioning Keys, Primary Keys, and Unique Keys”. The CREATE TABLE ... PARTITION BY rules for specifying the number of partitions also apply to ALTER TABLE ... PARTITION BY.
  ALTER TABLE ... PARTITION BY became available in MySQL 5.1.6.
  The partition_definition clause for ALTER TABLE ADD PARTITION supports the same options as the clause of the same name for the CREATE TABLE statement. (See Section 13.1.17, “CREATE TABLE Syntax”, for the syntax and description.) Suppose that you have the partitioned table created as shown here:

  CREATE TABLE t1 (
      id INT,
      year_col INT
  )
  PARTITION BY RANGE (year_col) (
      PARTITION p0 VALUES LESS THAN (1991),
      PARTITION p1 VALUES LESS THAN (1995),
      PARTITION p2 VALUES LESS THAN (1999)
  );

  You can add a new partition p3 to this table for storing values less than 2002 as follows:

  ALTER TABLE t1 ADD PARTITION (PARTITION p3 VALUES LESS THAN (2002));

  DROP PARTITION can be used to drop one or more RANGE or LIST partitions. This statement cannot be used withHASH or KEY partitions; instead, use COALESCE PARTITION (see below). Any data that was stored in the dropped partitions named in the partition_names list is discarded. For example, given the table t1 defined previously, you can drop the partitions named p0 and p1 as shown here:

  ALTER TABLE t1 DROP PARTITION p0, p1;

  Note

  DROP PARTITION does not work with tables that use the NDBCLUSTER storage engine. See Section 18.3.1, “Management of RANGE and LIST Partitions”, and Section 17.1.6, “Known Limitations of MySQL Cluster”.
  ADD PARTITION and DROP PARTITION do not currently support IF [NOT] EXISTS.
  Renames of partitioned table are supported. You can rename individual partitions indirectly using ALTER TABLE ... REORGANIZE PARTITION; however, this operation makes a copy of the partition's data..
  COALESCE PARTITION can be used with a table that is partitioned by HASH or KEY to reduce the number of partitions by number. Suppose that you have created table t2 using the following definition:

  CREATE TABLE t2 (
      name VARCHAR (30),
      started DATE
  )
  PARTITION BY HASH( YEAR(started) )
  PARTITIONS 6;

  You can reduce the number of partitions used by t2 from 6 to 4 using the following statement:

  ALTER TABLE t2 COALESCE PARTITION 2;

  The data contained in the last number partitions will be merged into the remaining partitions. In this case, partitions 4 and 5 will be merged into the first 4 partitions (the partitions numbered 0, 1, 2, and 3).
  To change some but not all the partitions used by a partitioned table, you can use REORGANIZE PARTITION. This statement can be used in several ways:
  • To merge a set of partitions into a single partition. This can be done by naming several partitions in thepartition_names list and supplying a single definition for partition_definition.
  • To split an existing partition into several partitions. You can accomplish this by naming a single partition forpartition_names and providing multiple partition_definitions.
  • To change the ranges for a subset of partitions defined using VALUES LESS THAN or the value lists for a subset of partitions defined using VALUES IN.
  • This statement may also be used without the partition_names INTO (partition_definitions) option on tables that are automatically partitioned using HASH partitioning to force redistribution of data. (Currently, onlyNDBCLUSTER tables are automatically partitioned in this way.) This is useful in MySQL Cluster NDB 7.0 and later where, after you have added new MySQL Cluster data nodes online to an existing MySQL Cluster, you wish to redistribute existing MySQL Cluster table data to the new data nodes. In such cases, you should invoke the statement with the ONLINE option; in other words, as shown here:

    ALTER ONLINE TABLE table REORGANIZE PARTITION;
    

    You cannot perform other DDL concurrently with online table reorganization—that is, no other DDL statements can be issued while an ALTER ONLINE TABLE ... REORGANIZE PARTITION statement is executing. For more information about adding MySQL Cluster data nodes online, see Section 17.5.13, “Adding MySQL Cluster Data Nodes Online”.
    ALTER ONLINE TABLE ... REORGANIZE PARTITION does not work with tables which were created using theMAX_ROWS option, because it uses the constant MAX_ROWS value specified in the original CREATE TABLE statement to determine the number of partitions required, so no new partitions are created. Beginning with MySQL Cluster NDB 7.0.32 and MySQL Cluster NDB 7.1.21, you can use ALTER ONLINE TABLE ... MAX_ROWS=rows to increase the maxmimum number of rows for the table; after this, ALTER ONLINE TABLE ... REORGANIZE PARTITION can use this new, larger value to increase the number of partitions. The value of rows must be greater than the value specified for MAX_ROWS in the original CREATE TABLE statement for this to work.
    Attempting to use REORGANIZE PARTITION without the partition_names INTO (partition_definitions)option on explicitly partitioned tables results in the error REORGANIZE PARTITION without parameters can only be used on auto-partitioned tables using HASH partitioning.
  Note

  For partitions that have not been explicitly named, MySQL automatically provides the default names p0, p1, p2, and so on. As of MySQL 5.1.7, the same is true with regard to subpartitions.
  For more detailed information about and examples of ALTER TABLE ... REORGANIZE PARTITION statements, see Section 18.3.1, “Management of RANGE and LIST Partitions”.