15.1.9.1 ALTER TABLE Partition Operations

Partitioning-related clauses for ALTER TABLE can be used with partitioned tables for repartitioning, to add, drop, discard, import, merge, and split partitions, and to perform partitioning maintenance.

• 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 (for more detailed information, see Section 15.1.20, “CREATE TABLE Statement”), 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;

  MySQL supports an ALGORITHM option with [SUB]PARTITION BY [LINEAR] KEY. ALGORITHM=1 causes the server to use the same key-hashing functions as MySQL 5.1 when computing the placement of rows in partitions; ALGORITHM=2 means that the server employs the key-hashing functions implemented and used by default for new KEY partitioned tables in MySQL 5.5 and later. (Partitioned tables created with the key-hashing functions employed in MySQL 5.5 and later cannot be used by a MySQL 5.1 server.) Not specifying the option has the same effect as using ALGORITHM=2. This option is intended for use chiefly when upgrading or downgrading [LINEAR] KEY partitioned tables between MySQL 5.1 and later MySQL versions, or for creating tables partitioned by KEY or LINEAR KEY on a MySQL 5.5 or later server which can be used on a MySQL 5.1 server.

  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 26.6.1, “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.

  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 15.1.20, “CREATE TABLE Statement”, 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 later in this section). 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 NDB storage engine. See Section 26.3.1, “Management of RANGE and LIST Partitions”, and Section 25.2.7, “Known Limitations of NDB Cluster”.

  ADD PARTITION and DROP PARTITION do not currently support IF [NOT] EXISTS.

  The DISCARD PARTITION ... TABLESPACE and IMPORT PARTITION ... TABLESPACE options extend the Transportable Tablespace feature to individual InnoDB table partitions. Each InnoDB table partition has its own tablespace file (.ibd file). The Transportable Tablespace feature makes it easy to copy the tablespaces from a running MySQL server instance to another running instance, or to perform a restore on the same instance. Both options take a comma-separated list of one or more partition names. For example:

  ALTER TABLE t1 DISCARD PARTITION p2, p3 TABLESPACE;

  ALTER TABLE t1 IMPORT PARTITION p2, p3 TABLESPACE;

  When running DISCARD PARTITION ... TABLESPACE and IMPORT PARTITION ... TABLESPACE on subpartitioned tables, both partition and subpartition names are allowed. When a partition name is specified, subpartitions of that partition are included.

  The Transportable Tablespace feature also supports copying or restoring partitioned InnoDB tables. For more information, see Section 17.6.1.3, “Importing InnoDB Tables”.

  Renames of partitioned tables are supported. You can rename individual partitions indirectly using ALTER TABLE ... REORGANIZE PARTITION; however, this operation copies the partition's data.

  To delete rows from selected partitions, use the TRUNCATE PARTITION option. This option takes a list of one or more comma-separated partition names. Consider the table t1 created by this statement:

  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),
      PARTITION p3 VALUES LESS THAN (2003),
      PARTITION p4 VALUES LESS THAN (2007)
  );

  To delete all rows from partition p0, use the following statement:

  ALTER TABLE t1 TRUNCATE PARTITION p0;

  The statement just shown has the same effect as the following DELETE statement:

  DELETE FROM t1 WHERE year_col < 1991;

  When truncating multiple partitions, the partitions do not have to be contiguous: This can greatly simplify delete operations on partitioned tables that would otherwise require very complex WHERE conditions if done with DELETE statements. For example, this statement deletes all rows from partitions p1 and p3:

  ALTER TABLE t1 TRUNCATE PARTITION p1, p3;

  An equivalent DELETE statement is shown here:

  DELETE FROM t1 WHERE
      (year_col >= 1991 AND year_col < 1995)
      OR
      (year_col >= 2003 AND year_col < 2007);

  If you use the ALL keyword in place of the list of partition names, the statement acts on all table partitions.

  TRUNCATE PARTITION merely deletes rows; it does not alter the definition of the table itself, or of any of its partitions.

  To verify that the rows were dropped, check the INFORMATION_SCHEMA.PARTITIONS table, using a query such as this one:

  SELECT PARTITION_NAME, TABLE_ROWS
      FROM INFORMATION_SCHEMA.PARTITIONS
      WHERE TABLE_NAME = 't1';

  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 as follows:

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

  To reduce the number of partitions used by t2 from 6 to 4, use the following statement:

  ALTER TABLE t2 COALESCE PARTITION 2;

  The data contained in the last number partitions is merged into the remaining partitions. In this case, partitions 4 and 5 are 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 is 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. 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.

  Note

  For partitions that have not been explicitly named, MySQL automatically provides the default names p0, p1, p2, and so on. The same is true with regard to subpartitions.

  For more detailed information about and examples of ALTER TABLE ... REORGANIZE PARTITION statements, see Section 26.3.1, “Management of RANGE and LIST Partitions”.

• To exchange a table partition or subpartition with a table, use the ALTER TABLE ... EXCHANGE PARTITION statement—that is, to move any existing rows in the partition or subpartition to the nonpartitioned table, and any existing rows in the nonpartitioned table to the table partition or subpartition.

  Once one or more columns have been added to a partitioned table using ALGORITHM=INSTANT, it is no longer possible to exchange partitions with that table.

  For usage information and examples, see Section 26.3.3, “Exchanging Partitions and Subpartitions with Tables”.

• Several options provide 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; for more information, see Section 15.7.3, “Table Maintenance Statements”). 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 target table. You can also use the ALL keyword in place of partition_names, in which case the statement acts on all table partitions. For more information and examples, see Section 26.3.4, “Maintenance of Partitions”.

  InnoDB does not currently support per-partition optimization; ALTER TABLE ... OPTIMIZE PARTITION 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 ALTER TABLE ... REBUILD PARTITION and ALTER TABLE ... ANALYZE PARTITION instead.

  The ANALYZE PARTITION, CHECK PARTITION, OPTIMIZE PARTITION, and REPAIR PARTITION options are not supported for tables which are not partitioned.

• REMOVE PARTITIONING enables you to remove a table's partitioning without otherwise affecting the table or its data. This option can be combined with other ALTER TABLE options such as those used to add, drop, or rename columns or indexes.

• Using the ENGINE option with ALTER TABLE changes the storage engine used by the table without affecting the partitioning. The target storage engine must provide its own partitioning handler. Only the InnoDB and NDB storage engines have native partitioning handlers.

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. For more information, see Section 15.1.9.1, “ALTER TABLE Partition Operations”.

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, EXCHANGE 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;

REBUILD operations are currently unsupported for subpartitions. The REBUILD keyword is expressly disallowed with subpartitions, and causes ALTER TABLE to fail with an error if so used.

CHECK PARTITION and REPAIR PARTITION operations fail when the partition to be checked or repaired contains any duplicate key errors.

For more information about these statements, see Section 26.3.4, “Maintenance of Partitions”.