MySQL 5.1 Reference Manual  /  ...  /  ALTER TABLE Partition Operations

13.1.7.1 ALTER TABLE Partition Operations

A number of partitioning-related extensions to ALTER TABLE were added in MySQL 5.1.5. These can be used with partitioned tables for repartitioning, for adding, dropping, merging, and splitting partitions, and for performing partitioning maintenance.

It is possible for an ALTER TABLE statement to contain a PARTITION BY or REMOVE PARTITIONING clause in an addition to other alter specifications, but the PARTITION BY or REMOVE PARTITIONING clause must be specified last after any other specifications. The ADD PARTITION, DROP PARTITION, COALESCE PARTITION, REORGANIZE PARTITION, ANALYZE PARTITION, CHECK PARTITION, and REPAIR PARTITION options cannot be combined with other alter specifications in a single ALTER TABLE, since the options just listed act on individual partitions.

  • 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 with PARTITION BY, and follows the same syntax and other rules as apply to the partition_options clause for CREATE 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 with HASH 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 the partition_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 for partition_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, only NDBCLUSTER 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 the MAX_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 maximum 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”.

  • Several additional options were introduced in MySQL 5.1.5 for providing partition maintenance and repair functionality analogous to that implemented for nonpartitioned tables by statements such as CHECK TABLE and REPAIR TABLE (which are also supported for partitioned tables, beginning with MySQL 5.1.27—see note at the end of this item). These include ANALYZE PARTITION, CHECK PARTITION, OPTIMIZE PARTITION, REBUILD PARTITION, and REPAIR PARTITION. Each of these options takes a partition_names clause consisting of one or more names of partitions, separated by commas. The partitions must already exist in the table to be altered. You can also use the ALL keyword in place of partition_names, in which case the statement acts on all partitions in the table. For more information and examples, see Section 18.3.3, “Maintenance of Partitions”.

    Prior to MySQL 5.1.68, it was not safe to execute multiple concurrent REBUILD TABLE operations on partitioned tables, whether on the same or different tables. (Bug #14589559, Bug #66645)

    Some MySQL storage engines, such as InnoDB, do not support per-partition optimization. For a partitioned table using such a storage engine, ALTER TABLE ... OPTIMIZE PARTITION rebuilds the entire table. This is a known issue. Beginning with MySQL 5.1.68, running this statement on such a table causes the entire table to rebuilt and analyzed, and an appropriate warning to be issued. (Bug #11751825, Bug #42822)

    To work around this problem, use the statements ALTER TABLE ... REBUILD PARTITION and ALTER TABLE ... ANALYZE PARTITION instead.

    The ANALYZE PARTITION, CHECK PARTITION, OPTIMIZE PARTITION, and REPAIR PARTITION options were disabled in MySQL 5.1.24, and re-enabled in MySQL 5.1.27. (Bug #20129) They are not supported for tables which are not partitioned; beginning with MySQL 5.1.31, they are not permitted for such tables.

    Beginning with MySQL 5.1.27, you can use the statements ANALYZE TABLE, CHECK TABLE, OPTIMIZE TABLE, and REPAIR TABLE on partitioned tables. See Section 13.7.2, “Table Maintenance Statements”, for more information.

  • REMOVE PARTITIONING was introduced in MySQL 5.1.8 for the purpose of removing a table's partitioning without otherwise affecting the table or its data. (Previously, this was done using the ENGINE option.) This option can be combined with other ALTER TABLE options such as those used to add, drop, or rename columns or indexes.

  • In MySQL 5.1.7 and earlier, using the ENGINE option with ALTER TABLE caused any partitioning that a table might have had to be removed. Beginning with MySQL 5.1.8, this option merely changes the storage engine used by the table and no longer affects partitioning in any way.

Only a single instance of any one of the following options can be used in a given ALTER TABLE statement: PARTITION BY, ADD PARTITION, DROP PARTITION, TRUNCATE PARTITION, REORGANIZE PARTITION, or COALESCE PARTITION, ANALYZE PARTITION, CHECK PARTITION, OPTIMIZE PARTITION, REBUILD PARTITION, REMOVE PARTITIONING.

For example, the following two statements are invalid:

ALTER TABLE t1 ANALYZE PARTITION p1, ANALYZE PARTITION p2;

ALTER TABLE t1 ANALYZE PARTITION p1, CHECK PARTITION p2;

In the first case, you can analyze partitions p1 and p2 of table t1 concurrently using a single statement with a single ANALYZE PARTITION option that lists both of the partitions to be analyzed, like this:

ALTER TABLE t1 ANALYZE PARTITION p1, p2;

In the second case, it is not possible to perform ANALYZE and CHECK operations on different partitions of the same table concurrently. Instead, you must issue two separate statements, like this:

ALTER TABLE t1 ANALYZE PARTITION p1;
ALTER TABLE t1 CHECK PARTITION p2;

ANALYZE, CHECK, OPTIMIZE, REBUILD, REPAIR, and TRUNCATE operations are not allowed with subpartitions.


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