Pre-General Availability Draft: 2018-02-22
Partitioning-related clauses for
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
ALTER TABLEon 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
CREATE TABLE(for more detailed information, see Section 13.1.18, “CREATE TABLE Syntax”), 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
idcolumn as the partitioning key, into 8 partitions by means of this statement:
ALTER TABLE t1 PARTITION BY HASH(id) PARTITIONS 8;
MySQL supports an
[SUB]PARTITION BY [LINEAR] KEY.
ALGORITHM=1causes the server to use the same key-hashing functions as MySQL 5.1 when computing the placement of rows in partitions;
ALGORITHM=2means that the server employs the key-hashing functions implemented and used by default for new
KEYpartitioned 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] KEYpartitioned tables between MySQL 5.1 and later MySQL versions, or for creating tables partitioned by
LINEAR KEYon 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 BYstatement 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 23.6.1, “Partitioning Keys, Primary Keys, and Unique Keys”. The
CREATE TABLE ... PARTITION BYrules for specifying the number of partitions also apply to
ALTER TABLE ... PARTITION BY.
ALTER TABLE ADD PARTITIONsupports the same options as the clause of the same name for the
CREATE TABLEstatement. (See Section 13.1.18, “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
p3to this table for storing values less than
ALTER TABLE t1 ADD PARTITION (PARTITION p3 VALUES LESS THAN (2002));
ADD PARTITIONcan also be used with the
TABLESPACEclause to add a new partition to an existing general tablespace, to a file-per-table tablespace, or to the system tablespace.
ALTER TABLE t1 ADD PARTITION (PARTITION p4 VALUES LESS THAN (2015) TABLESPACE = `ts1`); ALTER TABLE t1 ADD PARTITION (PARTITION p4 VALUES LESS THAN (2015) TABLESPACE = `innodb_file_per_table`); ALTER TABLE t1 ADD PARTITION (PARTITION p4 VALUES LESS THAN (2015) TABLESPACE = `innodb_system`);Note
TABLESPACE =option is not defined, the
ALTER TABLE ... ADD PARTITIONoperation adds the partition to the table's default tablespace, which can be specified at the table level during
DROP PARTITIONcan be used to drop one or more
LISTpartitions. This statement cannot be used with
KEYpartitions; instead, use
COALESCE PARTITION(see later in this section). Any data that was stored in the dropped partitions named in the
partition_nameslist is discarded. For example, given the table
t1defined previously, you can drop the partitions named
p1as shown here:
ALTER TABLE t1 DROP PARTITION p0, p1;
DROP PARTITIONdo not currently support
IF [NOT] EXISTS.
DISCARD PARTITION ... TABLESPACEand
IMPORT PARTITION ... TABLESPACEoptions extend the Transportable Tablespace feature to individual
InnoDBtable partitions. Each
InnoDBtable partition has its own tablespace file (
.idbfile). 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;
DISCARD PARTITION ... TABLESPACEand
IMPORT PARTITION ... TABLESPACEon 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
InnoDBtables (all partitions at once). For additional information, see Section 15.7.6, “Copying File-Per-Table Tablespaces to Another Instance”, as well as, Section 18.104.22.168, “Transportable Tablespace Examples”.
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 PARTITIONoption. This option takes a list of one or more comma-separated partition names. Consider the table
t1created 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 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
WHEREconditions if done with
DELETEstatements. For example, this statement deletes all rows from partitions
ALTER TABLE t1 TRUNCATE PARTITION p1, p3;
DELETEstatement 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
ALLkeyword in place of the list of partition names, the statement acts on all table partitions.
TRUNCATE PARTITIONmerely 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.PARTITIONStable, using a query such as this one:
SELECT PARTITION_NAME, TABLE_ROWS FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME = 't1';
COALESCE PARTITIONcan be used with a table that is partitioned by
KEYto reduce the number of partitions by
number. Suppose that you have created table
CREATE TABLE t2 ( name VARCHAR (30), started DATE ) PARTITION BY HASH( YEAR(started) ) PARTITIONS 6;
To reduce the number of partitions used by
t2from 6 to 4, use the following statement:
ALTER TABLE t2 COALESCE PARTITION 2;
The data contained in the last
numberpartitions 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 is done by naming several partitions in the
partition_nameslist and supplying a single definition for
To split an existing partition into several partitions. Accomplish this by naming a single partition for
partition_namesand providing multiple
To change the ranges for a subset of partitions defined using
VALUES LESS THANor the value lists for a subset of partitions defined using
To move a partition from one tablespace to another. For an example, see Moving Table Partitions Between Tablespaces Using ALTER TABLE.
For partitions that have not been explicitly named, MySQL automatically provides the default names
p2, and so on. The same is true with regard to subpartitions.
For more detailed information about and examples of
ALTER TABLE ... REORGANIZE PARTITIONstatements, see Section 23.3.1, “Management of RANGE and LIST Partitions”.
To exchange a table partition or subpartition with a table, use the
ALTER TABLE ... EXCHANGE PARTITIONstatement—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 23.3.3, “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
REPAIR TABLE(which are also supported for partitioned tables; for more information, see Section 13.7.3, “Table Maintenance Statements”). These include
REBUILD PARTITION, and
REPAIR PARTITION. Each of these options takes a
partition_namesclause 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
ALLkeyword in place of
partition_names, in which case the statement acts on all table partitions. For more information and examples, see Section 23.3.4, “Maintenance of Partitions”.
InnoDBdoes not currently support per-partition optimization;
ALTER TABLE ... OPTIMIZE PARTITIONcauses 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 PARTITIONand
ALTER TABLE ... ANALYZE PARTITIONinstead.
OPTIMIZE PARTITION, and
REPAIR PARTITIONoptions are not supported for tables which are not partitioned.
REMOVE PARTITIONINGenables you to remove a table's partitioning without otherwise affecting the table or its data. This option can be combined with other
ALTER TABLEoptions such as those used to add, drop, or rename columns or indexes.
ALTER TABLEchanges the storage engine used by the table without affecting the partitioning. The target storage engine must provide its own partitioning handler. Only the
NDBstorage engines have native partitioning handlers;
NDBis not currently supported in MySQL 8.0.
It is possible for an
statement to contain a
PARTITION BY or
REMOVE PARTITIONING clause in an addition to
other alter specifications, but the
REMOVE PARTITIONING clause
must be specified last after any other specifications.
CHECK PARTITION, and
REPAIR PARTITION options cannot be combined
with other alter specifications in a single
TABLE, since the options just listed act on individual
partitions. For more information, see
Section 22.214.171.124, “ALTER TABLE Partition Operations”.
Only a single instance of any one of the following options can
be used in a given
REORGANIZE PARTITION, or
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
p2 of table
t1 concurrently using a single statement with
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
operations on different partitions of the same table
concurrently. Instead, you must issue two separate statements,
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
PARTITION operations fail when the partition to be
checked or repaired contains any duplicate key errors.
For more information about these statements, see Section 23.3.4, “Maintenance of Partitions”.