ALTER TABLE Partition Operations

Partitioning-related clauses for ALTER TABLE can be used with partitioned tables for repartitioning, for adding, dropping, merging, and splitting partitions, and for performing 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 (see , "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 , "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 , "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;
  

  ADD PARTITION and DROP PARTITION do not currently support IF [NOT] EXISTS. It is also not possible to rename a partition or a partitioned table. Instead, if you wish to rename a partition, you must drop and re-create the partition; if you wish to rename a partitioned table, you must instead drop all partitions, rename the table, and then add back the partitions that were dropped.

  In MariaDB 5.6, it is possible to delete rows from selected partitions using the TRUNCATE PARTITION option. This option takes a comma-separated list of one or more partition names. For example, consider the table t1 as defined 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),
   PARTITION p3 VALUES LESS THAN (2003),
   PARTITION p4 VALUES LESS THAN (2007)
  );
  

  To delete all rows from partition p0, you can 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);
  

  You can also use the ALL keyword in place of the list of partition names; in this case, the statement acts on all partitions in the table.

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

  TRUNCATE PARTITION does not work with subpartitions.

  You can verify that the rows were dropped by checking 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';
  

  TRUNCATE PARTITION is supported only for partitioned tables that use the MyISAM, InnoDB, or MEMORY storage engine. It also works on BLACKHOLE tables (but has no effect). It is not supported for ARCHIVE tables.

  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.
  Note

  For partitions that have not been explicitly named, MariaDB 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 , "Management of RANGE and LIST Partitions".

• It is also possible in MariaDB 5.6 to exchange a table partition or subpartition with a table using ALTER TABLE pt EXCHANGE PARTITION p WITH TABLE nt, where pt is the partitioned table and p is the partition or subpartition of pt to be exchanged with unpartitioned table nt, provided that the following statements are true:
  
  
  1. Table nt is not itself partitioned.
  2. The structures of tables pt and nt are otherwise identical.
  3. There are no rows in nt that lie outside the boundaries of the partition definition for p.
  4. Table nt contains no foreign key references, and no other table has any foreign keys that refer to nt.

  Executing ALTER TABLE ... EXCHANGE PARTITION does not invoke any triggers on either the partitioned table or the table to be exchanged.

  Any AUTO_INCREMENT columns in the table to be exchanged with a partition are reset.

  The IGNORE keyword has no effect when used with ALTER TABLE ... EXCHANGE PARTITION.

  For more information about and examples of ALTER TABLE ... EXCHANGE PARTITION, see , "Exchanging Partitions and Subpartitions with Tables".

• Several additional 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; see , "Table Maintenance Statements" for more information). 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 , "Maintenance of Partitions".
  

  The ANALYZE PARTITION, CHECK PARTITION, OPTIMIZE PARTITION, and REPAIR PARTITION options are not permitted 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 drop columns or indexes.
• Using the ENGINE option with ALTER TABLE changes the storage engine used by the table without affecting the partitioning.

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:

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