ALTER TABLE PARTITION

Function

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

Compared with the kernel syntax, the rebuild, remove, check, repair, optimize, truncate, analyze, exchange of Dolphin is modified in B compatibility mode.

Precautions

The tablespace of the added partition cannot be PG_GLOBAL.
The name of the added partition must be different from the names of existing partitions in the partitioned table.
The key value of the added partition must be consistent with the type of partition keys in the partitioned table.
If a range partition is added, the key value of the added partition must be greater than the upper limit of the last range partition in the partitioned table.
If a list partition is added, the key value of the added partition cannot be the same as that of an existing partition.
Hash partitions cannot be added.
If the number of partitions in the target partitioned table has reached the maximum (1048575), partitions cannot be added.
If a partitioned 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 partitions, and they must be consistent.
The Value partitioned 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 splitting, combination, addition, and deletion of partitions.
List partitioned tables do not support partition splitting or partition combination.
Only the owner of a partitioned table or users granted with the ALTER permission on the partitioned table can run the ALTER TABLE PARTITION command. The system administrator has the permission to run the command 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 partition continuity, when multiple clauses are used for partition maintenance, openGauss performs 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  |
    truncate_clause |
    rebuild_clause |
    remove_clause |
    repair_clause |
    check_clause |
    optimize_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 an ordinary 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 ] [ UPDATE GLOBAL INDEX ]
```
  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 compressed information of the ordinary table and partitioned table 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.
  - An ordinary table cannot be a temporary table. A partitioned table can only be a range partitioned table, list partitioned table, or hash partitioned table.
  - Ordinary tables and partitioned tables do not support dynamic data masking and row-level access control constraints.
  - List partitioned tables and hash partitioned tables cannot be column-store.
  - List, hash, and range partitioned tables support exchange_clause.
  NOTICE:
  - When the exchange is done, the data and tablespace of the ordinary table and partition are exchanged. The statistics about ordinary tables and partitions become unreliable, and they should be analyzed again.
  - A non-partition key cannot be used to create a local unique index. Therefore, if an ordinary table contains a unique index, data cannot be exchanged.
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 ] [ UPDATE GLOBAL INDEX ]

The modify_clause syntax is used to set whether a partitioned index is available.

MODIFY PARTITION partition_name { UNUSABLE LOCAL INDEXES | REBUILD UNUSABLE LOCAL INDEXES }

The split_clause syntax is used to split one partition into different partitions.

SPLIT PARTITION { partition_name | FOR ( partition_value [, ...] ) } { split_point_clause | no_split_point_clause } [ UPDATE GLOBAL INDEX ]

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_less_than_item should equal that of the partition being split.
- The start point (if any) of the first new partition specified by partition_start_end_item must be equal to the partition key (if any) of the previous partition. The end point (if any) of the last partition specified by partition_start_end_item must be equal to the partition key of the splitting partition.
- 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. There is no restriction on different split statements.

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 START END.

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 ( partition_col1_name = partition_col1_value [, partition_col2_name = partition_col2_value ] [, ...] )
        [ LOCATION 'location1' ]
        [ PARTITION (partition_colA_name = partition_colA_value [, partition_colB_name = partition_colB_value ] [, ...] ) ]
        [ LOCATION 'location2' ]
    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 supported data types, 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 [, ...] )  } [ UPDATE GLOBAL INDEX ]
```
NOTICE: Hash partitioned table does not support partition deletion.

The truncate_clause syntax is used to remove a specified partition from a partitioned table.

TRUNCATE PARTITION  { partition_name | FOR (  partition_value [, ...] )  } [ UPDATE GLOBAL INDEX ]

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;

The syntax for recreating a partition is as follows: It is generally used to reclaim the space used by a partition, which has the same effect as deleting all records stored in the partition and then inserting them again. This is useful for defragmentation.
Column-store tables are not supported, and level-2 partitions of level-2 partitioned tables cannot be specified.
```
REBUILD PARTITION  { partition_name } [, ...]
REBUILD PARTITION ALL
```
The syntax for removing partitions from a table is as follows: Partitions are removed from a table but all data is retained.
Column-store tables and segment tables are not supported.
```
REMOVE PARTITIONING
```

The syntax for repairing, checking, and optimizing partitioned tables is as follows: It is used only for syntax and has no actual purpose.

CHECK PARTITION { partition_name } [, ...]
CHECK PARTITION ALL
REPAIR PARTITION { partition_name } [, ...]
REPAIR PARTITION ALL
OPTIMIZE PARTITION { partition_name } [, ...]
OPTIMIZE PARTITION ALL

The syntax for truncating partitions in a B-compatible database is as follows: The truncate operation deletes all data corresponding to the current partition.
```
TRUNCATE PARTITION { partition_name } [, ...]
TRUNCATE PARTITION all
```
The syntax for exchanging partitions in a B-compatible database is as follows: It can be used to exchange data between partitioned tables and ordinary tables. Data in ordinary tables and partitions is exchanged, and tablespace information in ordinary tables and partitions is exchanged. In this case, the statistics of ordinary tables and partitions become unreliable. You need to run ANALYZE on ordinary tables and partitions again.
Level-2 partitions cannot be exchanged.
```
exchange partition partition_name with table table_name (without/with validation);
```
The syntax for analyzing partitions in a B-compatible database is as follows: It collects statistics related to table contents. The execution plan generator uses the statistics to determine the most effective execution plan.
Level-2 partitions cannot be specified using ANALYZE.
```
analyze partition { partition_name } [, ...]
analyze partition all;
```

The syntax for adding partitions in a B-compatible database is as follows:

ADD {partition_less_than_item | partition_start_end_item| partition_list_item } [, ...]

The syntax for dropping partitions in a B-compatible database is as follows:

DROP PARTITION { { partition_name } [ UPDATE GLOBAL INDEX ] } [, ...]
DROP SUBPARTITION { { partition_name } [ UPDATE GLOBAL INDEX ] } [, ...]

The syntax for reorganizing partitions in a B-compatible database is as follows: It splits or merges specified partitions to reorganize the definition of partitions.
Here are some key points for ALTER TABLE… REORGANIZE PARTITION to repartition:
- The options used by PARTITION to determine the new partitioning scheme should follow the same rules as those used by the CREATE TABLE statement.
- The new RANGE partitioning scheme cannot have any overlapping scope. A new LIST partitioning scheme cannot have any overlapping value sets.
- The partition combination in the partition_definitions list should have the same range or overall value set partition_list as the composite partition named in the list.
- For a table RANGE with partitions, you can only reorganize adjacent partitions. You cannot skip range partitions.
- For the LIST partition, the value definition of the corresponding data cannot be deleted.
- REORGANIZE PARTITION cannot be used to change the partition type used by a table.
- The original table data cannot be lost.
- The interval partition and value partition are not supported.
```
REORGANIZE PARTITION {{ partition_name } [, ...]} INTO {partition_less_than_item | partition_list_item } [, ...]
```

Parameter Description

table_name
Specifies the name of a partitioned table.
Value range: an existing partitioned table name.
partition_name
Specifies the name of a partition.
Value range: an existing partition name.
tablespacename
Specifies which tablespace the partition moves to.
Value range: an existing tablespace name
partition_value
Partition key value
Values 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 operation, the partition where the tuple is located is altered. Setting of 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 exchanged.
Value range:
- WITH: checks whether the common table data meets the partition key range of the partition to be exchanged. If any data does not meet the required range, an error is reported.
- WITHOUT: does not check whether the common table data meets the partition key range of the partition to be exchanged.
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: String, which must comply with the naming convention.

Examples

For details, see Examples in CREATE TABLE PARTITION.

Helpful Links

CREATE TABLE PARTITION, DROP TABLE