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 withALTER TABLE
on a partitioned table repartitions the table according to the partitioning scheme defined by thepartition_options
. This clause always begins withPARTITION BY
, and follows the same syntax and other rules as apply to thepartition_options
clause forCREATE TABLE
(for more detailed information, see Section 13.1.18, “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 theid
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 newKEY
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 usingALGORITHM=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 byKEY
orLINEAR KEY
on a MySQL 5.5 or later server which can be used on a MySQL 5.1 server.To upgrade a
KEY
partitioned table that was created in MySQL 5.1, first executeSHOW CREATE TABLE
and note the exact columns and number of partitions shown. Now execute anALTER TABLE
statement using exactly the same column list and number of partitions as in theCREATE TABLE
statement, while addingALGORITHM=2
immediately following thePARTITION BY
keywords. (You should also include theLINEAR
keyword if it was used for the original table definition.) An example from a session in the mysql client is shown here:mysql> SHOW CREATE TABLE p\G *************************** 1. row *************************** Table: p Create Table: CREATE TABLE `p` ( `id` int(11) NOT NULL AUTO_INCREMENT, `cd` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 /*!50100 PARTITION BY LINEAR KEY (id) PARTITIONS 32 */ 1 row in set (0.00 sec) mysql> ALTER TABLE p PARTITION BY LINEAR KEY ALGORITHM=2 (id) PARTITIONS 32; Query OK, 0 rows affected (5.34 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> SHOW CREATE TABLE p\G *************************** 1. row *************************** Table: p Create Table: CREATE TABLE `p` ( `id` int(11) NOT NULL AUTO_INCREMENT, `cd` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 /*!50100 PARTITION BY LINEAR KEY (id) PARTITIONS 32 */ 1 row in set (0.00 sec)
Downgrading a table created using the default key-hashing used in MySQL 5.5 and later to enable its use by a MySQL 5.1 server is similar, except in this case you should use
ALGORITHM=1
to force the table's partitions to be rebuilt using the MySQL 5.1 key-hashing functions. It is recommended that you not do this except when necessary for compatibility with a MySQL 5.1 server, as the improvedKEY
hashing functions used by default in MySQL 5.5 and later provide fixes for a number of issues found in the older implementation.NoteA table upgraded by means of
ALTER TABLE ... PARTITION BY ALGORITHM=2 [LINEAR] KEY ...
can no longer be used by a MySQL 5.1 server. (Such a table would need to be downgraded withALTER TABLE ... PARTITION BY ALGORITHM=1 [LINEAR] KEY ...
before it could be used again by 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 usingCREATE 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 22.6.1, “Partitioning Keys, Primary Keys, and Unique Keys”. TheCREATE TABLE ... PARTITION BY
rules for specifying the number of partitions also apply toALTER TABLE ... PARTITION BY
.The
partition_definition
clause forALTER TABLE ADD PARTITION
supports the same options as the clause of the same name for theCREATE TABLE
statement. (See Section 13.1.18, “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 than2002
as follows:ALTER TABLE t1 ADD PARTITION (PARTITION p3 VALUES LESS THAN (2002));
DROP PARTITION
can be used to drop one or moreRANGE
orLIST
partitions. This statement cannot be used withHASH
orKEY
partitions; instead, useCOALESCE PARTITION
(see below). Any data that was stored in the dropped partitions named in thepartition_names
list is discarded. For example, given the tablet1
defined previously, you can drop the partitions namedp0
andp1
as shown here:ALTER TABLE t1 DROP PARTITION p0, p1;
NoteDROP PARTITION
does not work with tables that use theNDB
storage engine. See Section 22.3.1, “Management of RANGE and LIST Partitions”, and Section 21.2.7, “Known Limitations of NDB Cluster”.ADD PARTITION
andDROP PARTITION
do not currently supportIF [NOT] EXISTS
.DISCARD PARTITION ... TABLESPACE
andIMPORT PARTITION ... TABLESPACE
options extend the Transportable Tablespace feature to individualInnoDB
table partitions. EachInnoDB
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 list of one or more comma-separated 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
andIMPORT 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 14.6.1.3, “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 comma-separated list of one or more partition names. For example, consider the tablet1
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
, 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 withDELETE
statements. For example, this statement deletes all rows from partitionsp1
andp3
: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';
TRUNCATE PARTITION
is supported only for partitioned tables that use theMyISAM
,InnoDB
, orMEMORY
storage engine. It also works onBLACKHOLE
tables (but has no effect). It is not supported forARCHIVE
tables.COALESCE PARTITION
can be used with a table that is partitioned byHASH
orKEY
to reduce the number of partitions bynumber
. Suppose that you have created tablet2
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 are 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 forpartition_definition
.To split an existing partition into several partitions. Accomplish this by naming a single partition for
partition_names
and providing multiplepartition_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 usingVALUES IN
.This statement may also be used without the
option on tables that are automatically partitioned usingpartition_names
INTO (partition_definitions
)HASH
partitioning to force redistribution of data. (Currently, onlyNDB
tables are automatically partitioned in this way.) This is useful in NDB Cluster where, after you have added new NDB Cluster data nodes online to an existing NDB Cluster, you wish to redistribute existing NDB Cluster table data to the new data nodes. In such cases, you should invoke the statement with theALGORITHM=INPLACE
option; in other words, as shown here:ALTER TABLE table ALGORITHM=INPLACE, REORGANIZE PARTITION;
You cannot perform other DDL concurrently with online table reorganization—that is, no other DDL statements can be issued while an
ALTER TABLE ... ALGORITHM=INPLACE, REORGANIZE PARTITION
statement is executing. For more information about adding NDB Cluster data nodes online, see Section 21.6.7, “Adding NDB Cluster Data Nodes Online”.NoteALTER TABLE ... ALGORITHM=INPLACE, REORGANIZE PARTITION
does not work with tables which were created using theMAX_ROWS
option, because it uses the constantMAX_ROWS
value specified in the originalCREATE TABLE
statement to determine the number of partitions required, so no new partitions are created. Instead, you can useALTER TABLE ... ALGORITHM=INPLACE, MAX_ROWS=
to increase the maximum number of rows for such a table; in this case,rows
ALTER TABLE ... ALGORITHM=INPLACE, REORGANIZE PARTITION
is not needed (and causes an error if executed). The value ofrows
must be greater than the value specified forMAX_ROWS
in the originalCREATE TABLE
statement for this to work.Employing
MAX_ROWS
to force the number of table partitions is deprecated in NDB 7.5.4 and later; usePARTITION_BALANCE
instead (see Setting NDB_TABLE options).Attempting to use
REORGANIZE PARTITION
without the
option on explicitly partitioned tables results in the error REORGANIZE PARTITION without parameters can only be used on auto-partitioned tables using HASH partitioning.partition_names
INTO (partition_definitions
)
NoteFor 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 22.3.1, “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.For usage information and examples, see Section 22.3.3, “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
andREPAIR TABLE
(which are also supported for partitioned tables; for more information, see Section 13.7.2, “Table Maintenance Statements”). These includeANALYZE PARTITION
,CHECK PARTITION
,OPTIMIZE PARTITION
,REBUILD PARTITION
, andREPAIR PARTITION
. Each of these options takes apartition_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 theALL
keyword in place ofpartition_names
, in which case the statement acts on all table partitions. For more information and examples, see Section 22.3.4, “Maintenance of Partitions”.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
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
andALTER TABLE ... ANALYZE PARTITION
instead.The
ANALYZE PARTITION
,CHECK PARTITION
,OPTIMIZE PARTITION
, andREPAIR PARTITION
options are not permitted for tables which are not partitioned.In MySQL 5.7.9 and later, you can use
ALTER TABLE ... UPGRADE PARTITIONING
to upgrade a partitionedInnoDB
table that was created with the old generic partitioning handler to theInnoDB
native partitioning employed in MySQL 5.7.6 and later. Also beginning with MySQL 5.7.9, the mysql_upgrade utility checks for such partitionedInnoDB
tables and attempts to upgrade them to native partitioning as part of its normal operations.ImportantPartitioned
InnoDB
tables that do not use theInnoDB
native partitioning handler cannot be used in MySQL 8.0 or later.ALTER TABLE ... UPGRADE PARTITIONING
is not supported in MySQL 8.0 or later; therefore, any partitionedInnoDB
tables that employ the generic handler must be upgraded to the InnoDB native handler before upgrading your MySQL installation to MySQL 8.0 or later.REMOVE PARTITIONING
enables you to remove a table's partitioning without otherwise affecting the table or its data. This option can be combined with otherALTER TABLE
options such as those used to add, drop, or rename columns or indexes.Using the
ENGINE
option withALTER TABLE
changes the storage engine used by the table without affecting the partitioning.
When ALTER TABLE ... EXCHANGE PARTITION
or
ALTER TABLE ... TRUNCATE PARTITION
is run
against a partitioned table that uses
MyISAM
(or another storage engine
that makes use of table-level locking), only those partitions
that are actually read from are locked. (This does not apply to
partitioned tables using a storage enginethat employs row-level
locking, such as InnoDB
.) See
Section 22.6.4, “Partitioning and Locking”.
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 13.1.8.1, “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 22.3.4, “Maintenance of Partitions”.