ALTER TABLE PARTITION

Function

ALTER TABLE PARTITION modifies table partition, including adding, deleting, splitting, merging partitions, and modifying partition attributes.

Precautions

The tablespace for the added partition cannot be PG_GLOBAL.
The name of the added partition must be different from names of existing partitions in the partition table.
The partition key of the added partition must be the same type as that of the partition table. The key value of the added partition must exceed the upper limit of the last partition range.
If the number of partitions in the target partitioned table has reached the maximum value, no more partitions can be added. (The maximum number of partitions in a range partitioned table is 32767, and that in a hash or list partitioned table is 64.)
If a partition table has only one partition, the partition cannot be deleted.
Use PARTITION FOR() to choose partitions. The number of specified values in the brackets should be the same as the column number in customized partition, and they must be consistent.
The Value partition table does not support the Alter Partition operation.
Column-store tables and row-store tables do not support partition splitting.
Partitions cannot be added to an interval partitioned table.
Hash partitioned tables do not support table partition modification.
List partitioned table supports only partition addition or deletion.
Only the partitioned table owner or a user granted with the ALTER permission can run the ALTER TABLE PARTITION command. The system administrator has this permission by default.

Syntax

Modify the syntax of the table partition.
```
ALTER TABLE [ IF EXISTS ] { table_name  [*] | ONLY table_name | ONLY ( table_name  )}
    action [, ... ];
```
action indicates the following clauses for maintaining partitions. For the partition continuity when multiple clauses are used for partition maintenance, openGauss does DROP PARTITION and then ADD PARTITION, and finally runs the rest clauses in sequence.
```
move_clause  |
    exchange_clause  |
    row_clause  |
    merge_clause  |
    modify_clause  |
    split_clause  |
    add_clause  |
    drop_clause
```
- The move_clause syntax is used to move the partition to a new tablespace.
```
MOVE PARTITION { partion_name | FOR ( partition_value [, ...] ) } TABLESPACE tablespacename
```
- The exchange_clause syntax is used to move the data from a general table to a specified partition.
```
EXCHANGE PARTITION { ( partition_name ) | FOR ( partition_value [, ...] ) } 
    WITH TABLE {[ ONLY ] ordinary_table_name | ordinary_table_name * | ONLY ( ordinary_table_name )} 
    [ { WITH | WITHOUT } VALIDATION ] [ VERBOSE ]
```
  The ordinary table and partition whose data is to be exchanged must meet the following requirements:
  - The number of columns of the ordinary table is the same as that of the partition, and their information should be consistent, including: column name, data type, constraint, collation information, storage parameter, and compression information.
  - The compression information of the ordinary table and partition should be consistent.
  - The distribution key information of the ordinary table and partition should be consistent.
  - The number and information of indexes of the ordinary table and partition should be consistent.
  - The number and information of constraints of the ordinary table and partition should be consistent.
  - The ordinary table cannot be a temporary table.
  When the exchange is done, the data and tablespace of the ordinary table and partition are exchanged. The statistics of the ordinary table and partition are no longer inaccurate after the exchange, and they should be analyzed again.
- The row_clause syntax is used to set row movement of a partitioned table.
```
{ ENABLE | DISABLE } ROW MOVEMENT
```
- The merge_clause syntax is used to merge partitions into one.
```
MERGE PARTITIONS { partition_name } [, ...] INTO PARTITION partition_name 
    [ TABLESPACE tablespacename ]
```
- The modify_clause syntax is used to set whether a partition index is usable.
```
MODIFY PARTITION partition_name { UNUSABLE LOCAL INDEXES | REBUILD UNUSABLE LOCAL INDEXES }
```
- The split_clause syntax is used to split one partition into partitions.
```
SPLIT PARTITION { partition_name | FOR ( partition_value [, ...] ) } { split_point_clause | no_split_point_clause }
```
  - The split_point_clause syntax is used to specify a split point.
```
AT ( partition_value ) INTO ( PARTITION partition_name [ TABLESPACE tablespacename ] , PARTITION partition_name [ TABLESPACE tablespacename ] )
```
    NOTICE:
    - Column-store tables and row-store tables cannot be partitioned.
    - The size of the split point should be in the range of partition keys of the partition to be split. The split point can only split one partition into two new partitions.
  - The no_split_point_clause syntax does not specify a split point.
```
INTO { ( partition_less_than_item [, ...] ) | ( partition_start_end_item [, ...] ) }
```
    NOTICE:
    - The first new partition key specified by partition_less_than_item should be greater than that of the previously split partition (if any), and the last partition key specified by partition_item_clause should equal that of the partition being split.
    - The first new partition key specified by partition_start_end_item should equal that of the former partition (if any), and the last partition key specified by partition_start_end_item should equal that of the partition being split.
    - partition_less_than_item supports a maximum of 4 partition keys, while partition_start_end_item supports only one partition key. For details about the supported data types, see PARTITION BY RANGE(parti….
    - partition_less_than_item and partition_start_end_item cannot be used in the same statement.
  - The syntax of partition_less_than_item is as follows:
```
PARTITION partition_name VALUES LESS THAN ( { partition_value | MAXVALUE }  [, ...] ) 
    [ TABLESPACE tablespacename ]
```
  - The syntax of partition_start_end_item is as follows. For details about the constraints, see partition_start_end_item syntax.
```
PARTITION partition_name {
        {START(partition_value) END (partition_value) EVERY (interval_value)} |
        {START(partition_value) END ({partition_value | MAXVALUE})} |
        {START(partition_value)} |
        {END({partition_value | MAXVALUE})}
} [TABLESPACE tablespace_name]
```
- The add_clause syntax is used to add one or more partitions to a specified partitioned table.
```
ADD {partition_less_than_item | partition_start_end_item| partition_list_item }
```
  The syntax of partition_list_item is as follows:
```
PARTITION partition_name VALUES (list_values_clause) 
    [ TABLESPACE tablespacename ]
```
  NOTICE:
  - partition_list_item supports only one partition key. For details about the data types supported by partition_list_item, see PARTITION BY LIST(partit….
  - Interval and hash partitioned tables do not support partition addition.
- The drop_clause syntax is used to remove a partition from a specified partitioned table.
```
DROP PARTITION  { partition_name | FOR (  partition_value [, ...] )  } 
```
  NOTICE:
  - Hash partitioned table does not support partition deletion.
  - List partitioned table supports sub-partition deletion only by sub-partition name.

The syntax for modifying the name of a partition is as follows:

ALTER TABLE [ IF EXISTS ] { table_name [*] | ONLY table_name | ONLY ( table_name  )}
    RENAME PARTITION { partion_name | FOR ( partition_value [, ...] ) } TO partition_new_name;

Parameter Description

table_name
Specifies the name of a partitioned table.
Value range: an existing table name
partition_name
Specifies the name of a partition.
Value range: an existing table name
tablespacename
Specifies which tablespace the partition moves to.
Value range: an existing table name
partition_value
Specifies the key value of a partition.
The value specified by PARTITION FOR ( partition_value [, …] ) can uniquely identify a partition.
Value range: partition keys for the partition to be renamed
UNUSABLE LOCAL INDEXES
Sets all the indexes unusable in the partition.
REBUILD UNUSABLE LOCAL INDEXES
Rebuilds all the indexes in the partition.
ENABLE/DISABLE ROW MOVEMET
Sets row movement.
If the tuple value is updated on the partition key during the UPDATE action, the partition where the tuple is located is altered. Setting this parameter enables error messages to be reported or movement of the tuple between partitions.
Value range:
- ENABLE: Row movement is enabled.
- DISABLE: Row movement is disabled.
The default value is ENABLE.
ordinary_table_name
Specifies the name of the ordinary table whose data is to be migrated.
Value range: an existing table name
{ WITH | WITHOUT } VALIDATION
Checks whether the ordinary table data meets the specified partition key range of the partition to be migrated.
Value range:
- WITH: checks whether the ordinary table data meets the partition key range of the partition to be migrated. If any data does not meet the required range, an error is reported.
- WITHOUT: does not check whether the ordinary table data meets the partition key range of the partition to be migrated.
The default value is WITH.
The check is time consuming, especially when the data volume is large. Therefore, use WITHOUT when you are sure that the current ordinary table data meets the partition key range of the partition to be migrated.
VERBOSE
When VALIDATION is WITH, if the ordinary table contains data that is out of the partition key range, insert the data to the correct partition. If there is no correct partition where the data can be inserted to, an error is reported.
NOTICE: Only when VALIDATION is WITH, VERBOSE can be specified.
partition_new_name
Specifies the new name of a partition.
Value range: a string. It must comply with the naming convention.

Example

See Examples in CREATE TABLE PARTITION.

Helpful Links

CREATE TABLE PARTITION, and DROP TABLE