ALTER TABLE

Function

ALTER TABLE is used to modify tables, including modifying table definitions, renaming tables, renaming specified columns in tables, renaming table constraints, setting table schemas, enabling or disabling row-level access control, and adding or updating multiple columns.

Important Notes

• You must own the table to use ALTER TABLE. A system administrator has the permission by default.
• The storage parameter ORIENTATION cannot be modified.
• Currently, SET SCHEMA can only be used to set a schema to a user schema, not to a system internal schema.
• Column-store tables support PARTIAL CLUSTER KEY but do not support table-level foreign key constraints. In 8.1.1 or later, column-store tables support the PRIMARY KEY constraint and table-level UNIQUE constraint.
• In a column-store table, you can perform ADD COLUMN, ALTER TYPE, SET STATISTICS, DROP COLUMN operations. The types of new and modified columns should be the Data Types supported by column storage. The USING option of ALTER TYPE only supports constant expression and expression involved in the column.
• The column constraints supported by column-store tables include NULL, NOT NULL, and DEFAULT constant values. Only the DEFAULT value can be modified (SET DEFAULT and DROP DEFAULT), and only the NOT NULL constraint can be deleted. Currently, NULL and NOT NULL constraints cannot be modified.
• When you modify the COLVERSION or enable_delta parameter of a column-store table, other ALTER operations cannot be performed.

Syntax

• ALTER TABLE modifies the definition of a table.

  1 2	ALTER TABLE [ IF EXISTS ] { table_name [*] | ONLY table_name | ONLY ( table_name ) } action [, ... ];

  There are several clauses of action:

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

  column_clause | ADD table_constraint [ NOT VALID ] | ADD table_constraint_using_index | VALIDATE CONSTRAINT constraint_name | DROP CONSTRAINT [ IF EXISTS ] constraint_name [ RESTRICT | CASCADE ] | CLUSTER ON index_name | SET WITHOUT CLUSTER | SET ( {storage_parameter = value} [, ... ] ) | RESET ( storage_parameter [, ... ] ) | OWNER TO new_owner | SET TABLESPACE new_tablespace | SET {COMPRESS|NOCOMPRESS} | DISTRIBUTE BY { REPLICATION | { HASH ( column_name [,...] ) } } | TO { GROUP groupname | NODE ( nodename [, ... ] ) } | ADD NODE ( nodename [, ... ] ) | DELETE NODE ( nodename [, ... ] ) | DISABLE TRIGGER [ trigger_name | ALL | USER ] | ENABLE TRIGGER [ trigger_name | ALL | USER ] | ENABLE REPLICA TRIGGER trigger_name | ENABLE ALWAYS TRIGGER trigger_name | DISABLE ROW LEVEL SECURITY | ENABLE ROW LEVEL SECURITY | FORCE ROW LEVEL SECURITY | NO FORCE ROW LEVEL SECURITY | REFRESH STORAGE

  

  • ADD table_constraint [ NOT VALID ]

    Adds a new table constraint.

  • ADD table_constraint_using_index

    Adds primary key constraint or unique constraint based on the unique index.

  • VALIDATE CONSTRAINT constraint_name

    Validates a foreign key or check constraint that was previously created as NOT VALID, by scanning the table to ensure there are no rows for which the constraint is not satisfied. Nothing happens if the constraint is already marked valid.

  • DROP CONSTRAINT [ IF EXISTS ] constraint_name [ RESTRICT | CASCADE ]

    Drops a table constraint.

  • CLUSTER ON index_name

    Selects the default index for future CLUSTER operations. It does not actually re-cluster the table.

  • SET WITHOUT CLUSTER

    Removes the most recently used CLUSTER index specification from the table. This operation affects future cluster operations that do not specify an index.

  • SET ( {storage_parameter = value} [, ... ] )

    Changes one or more storage parameters for the table.

  • RESET ( storage_parameter [, ... ] )

    Resets one or more storage parameters to their defaults. As with SET, a table rewrite might be needed to update the table entirely.

  • OWNER TO new_owner

    Changes the owner of the table, sequence, or view to the specified user.

  • SET {COMPRESS|NOCOMPRESS}

    Sets the compression feature of a table. The table compression feature affects only the storage mode of data inserted in a batch subsequently and does not affect storage of existing data. Setting the table compression feature will result in the fact that there are both compressed and uncompressed data in the table.

  • DISTRIBUTE BY { REPLICATION | { HASH ( column_name [,...] ) } }

    Changing a table's distribution mode will physically redistribute the table data based on the new distribution mode. After the distribution mode is changed, you are advised to manually run the ANALYZE statement to collect new statistics about the table.

    

    • This operation is a major change operation, involving table distribution information modification and physical data redistribution. During the modification, services are blocked. After the modification, the original execution plan of services will change. Perform this operation according to the standard change process.
    • This operation is a resource-intensive operation. If you need to modify the distribution mode of large tables, perform the operation when the computing and storage resources are sufficient. Ensure that the remaining space of the entire cluster and the tablespace where the original table is located is sufficient to store a table that has the same size as the original table and is distributed in the new distribution mode.
  • TO { GROUP groupname | NODE ( nodename [, ... ] ) }

    The syntax is only available in extended mode (when GUC parameter support_extended_features is on). Exercise caution when enabling the mode. It is used for tools like internal dilatation tools. Common users should not use the mode.

  • ADD NODE ( nodename [, ... ] )

    It is only available for tools like internal dilatation. General users should not use the mode.

  • DELETE NODE ( nodename [, ... ] )

    It is only available for internal scale-in tools. Common users should not use the syntax.

  • DISABLE TRIGGER [ trigger_name | ALL | USER ]

    Disables a single trigger specified by trigger_name, disables all triggers, or disables only user triggers (excluding internally generated constraint triggers, for example, deferrable unique constraint triggers and exclusion constraints triggers).

    

    Exercise caution when using this function because data integrity cannot be ensured as expected if the triggers are not executed.

  • | ENABLE TRIGGER [ trigger_name | ALL | USER ]

    Enables a single trigger specified by trigger_name, enables all triggers, or enables only user triggers.

  • | ENABLE REPLICA TRIGGER trigger_name

    Determines that the trigger firing mechanism is affected by the configuration variable session_replication_role. When the replication role is origin (default value) or local, a simple trigger is fired.

    When ENABLE REPLICA is configured for a trigger, it is fired only when the session is in replica mode.

  • | ENABLE ALWAYS TRIGGER trigger_name

    Determines that all triggers are fired regardless of the current replication mode.

  • | DISABLE/ENABLE ROW LEVEL SECURITY

    Enables or disables row-level access control for a table.

    If row-level access control is enabled for a data table but no row-level access control policy is defined, the row-level access to the data table is not affected. If row-level access control for a table is disabled, the row-level access to the table is not affected even if a row-level access control policy has been defined. For details, see CREATE ROW LEVEL SECURITY POLICY.

  • | NO FORCE/FORCE ROW LEVEL SECURITY

    Forcibly enables or disables row-level access control for a table.

    By default, the table owner is not affected by the row-level access control feature. However, if row-level access control is forcibly enabled, the table owner (excluding system administrators) will be affected. System administrators are not affected by any row-level access control policies.

  • | REFRESH STORAGE

    Changes the local hot partitions that meet the criteria defined by the rules specified in the storage_policy parameter of an OBS hot or cold table to the cold partitions stored in the OBS.

    For example, if storage_policy is set to 'LMT:10' for an OBS hot or cold table when it is created, the partitions that are not updated within the last 10 days are switched to cold partitions in the OBS.

  • There are several clauses of column_clause:

    1 2 3 4 5 6 7 8 9 10 11 12 13 14

    ADD [ COLUMN ] column_name data_type [ compress_mode ] [ COLLATE collation ] [ column_constraint [ ... ] ] | MODIFY column_name data_type | MODIFY column_name [ CONSTRAINT constraint_name ] NOT NULL [ ENABLE ] | MODIFY column_name [ CONSTRAINT constraint_name ] NULL | DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ] | ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ] | ALTER [ COLUMN ] column_name { SET DEFAULT expression | DROP DEFAULT } | ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL | ALTER [ COLUMN ] column_name SET STATISTICS [PERCENT] integer | ADD STATISTICS (( column_1_name, column_2_name [, ...] )) | DELETE STATISTICS (( column_1_name, column_2_name [, ...] )) | ALTER [ COLUMN ] column_name SET ( {attribute_option = value} [, ... ] ) | ALTER [ COLUMN ] column_name RESET ( attribute_option [, ... ] ) | ALTER [ COLUMN ] column_name SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }

    

    • ADD [ COLUMN ] column_name data_type [ compress_mode ] [ COLLATE collation ] [ column_constraint [ ... ] ]

      Adds a column to a table. If a column is added with ADD COLUMN, all existing rows in the table are initialized with the column's default value (NULL if no DEFAULT clause is specified).

    • ADD ( { column_name data_type [ compress_mode ] } [, ...] )

      Adds columns in the table.

    • MODIFY column_name data_type

      Change the data type of an existing field in the table. Only the type conversion of the same category (between values, character strings, and time) is allowed.

    • MODIFY column_name [ CONSTRAINT constraint_name ] NOT NULL [ ENABLE ]

      Adds a NOT NULL constraint to a column of a table. Currently, this clause is unavailable to column-store tables.

    • MODIFY column_name [ CONSTRAINT constraint_name ] NULL

      Deletes the NOT NULL constraint to a certain column in the table.

    • DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ]

      Drops a column from a table. Index and constraint related to the column are automatically dropped. If an object not belonging to the table depends on the column, CASCADE must be specified, such as foreign key reference and view.

      The DROP COLUMN form does not physically remove the column, but simply makes it invisible to SQL operations. Subsequent insert and update operations in the table will store a NULL value for the column. Therefore, column deletion takes a short period of time but does not immediately release the table space on the disks, because the space occupied by the deleted column is not reclaimed. The space will be reclaimed when VACUUM is executed.

    • ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ]

      Change the data type of a field in the table. Only the type conversion of the same category (between values, character strings, and time) is allowed. Indexes and simple table constraints on the column will automatically use the new data type by reparsing the originally supplied expression.

      ALTER TYPE requires an entire table be rewritten. This is an advantage sometimes, because it frees up unnecessary space from a table. For example, to reclaim the space occupied by a deleted column, the fastest method is to use the command.

      1	ALTER TABLE table ALTER COLUMN anycol TYPE anytype;

      In this command, anycol indicates any column existing in the table and anytype indicates the type of the prototype of the column. ALTER TYPE does not change the table except that the table is forcibly rewritten. In this way, the data that is no longer used is deleted.

    • ALTER [ COLUMN ] column_name { SET DEFAULT expression | DROP DEFAULT }

      Sets or removes the default value for a column. The default values only apply to subsequent INSERT commands; they do not cause rows already in the table to change. Defaults can also be created for views, in which case they are inserted into INSERT statements on the view before the view's ON INSERT rule is applied.

    • ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL

      Changes whether a column is marked to allow NULL values or to reject NULL values. You can only use SET NOT NULL when the column contains no NULL values.

    • ALTER [ COLUMN ] column_name SET STATISTICS [PERCENT] integer

      Specifies the per-column statistics-gathering target for subsequent ANALYZE operations. The value ranges from 0 to 10000. Set it to -1 to revert to using the default system statistics target.

    • {ADD | DELETE} STATISTICS ((column_1_name, column_2_name [, ...]))

      Adds or deletes the declaration of collecting multi-column statistics to collect multi-column statistics as needed when ANALYZE is performed for a table or a database. The statistics about a maximum of 32 columns can be collected at a time. You are not allowed to add or delete the declaration for system tables or foreign tables

    • ALTER [ COLUMN ] column_name SET ( {attribute_option = value} [, ... ] )

      ALTER [ COLUMN ] column_name RESET ( attribute_option [, ... ] )

      Sets or resets per-attribute options.

      Currently, the only defined per-attribute options are n_distinct and n_distinct_inherited. n_distinct affects statistics of table, while n_distinct_inherited affects the statistics of table and its subtables. Currently, only SET/RESET n_distinct is supported, and SET/RESET n_distinct_inherited is forbidden.

    • ALTER [ COLUMN ] column_name SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }

      Sets the storage mode for a column. This clause specifies whether this column is held inline or in a secondary TOAST table, and whether the data should be compressed. This statement can only be used for row-based tables. SET STORAGE only sets the strategy to be used for future table operations.

    • column_constraint is as follows:

      1 2 3 4 5 6 7 8

      [ CONSTRAINT constraint_name ] { NOT NULL | NULL | CHECK ( expression ) | DEFAULT default_expr | UNIQUE index_parameters | PRIMARY KEY index_parameters } [ DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

    • compress_mode of a column is as follows:

      1	[ DELTA | PREFIX | DICTIONARY | NUMSTR | NOCOMPRESS ]

  • table_constraint_using_index used to add the primary key constraint or unique constraint based on the unique index is as follows:

    1 2 3

    [ CONSTRAINT constraint_name ] { UNIQUE | PRIMARY KEY } USING INDEX index_name [ DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

  • table_constraint is as follows:

    1 2 3 4 5 6

    [ CONSTRAINT constraint_name ] { CHECK ( expression ) | UNIQUE ( column_name [, ... ] ) index_parameters | PRIMARY KEY ( column_name [, ... ] ) index_parameters } [ DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

    index_parameters is as follows:

    1 2	[ WITH ( {storage_parameter = value} [, ... ] ) ] [ USING INDEX TABLESPACE tablespace_name ]

Parameter Description

• IF EXISTS

  Sends a notification instead of an error if no tables have identical names. The notification prompts that the table you are querying does not exist.

• table_name [*] | ONLY table_name | ONLY ( table_name )

  table_name is the name of table that you need to modify.

  If ONLY is specified, only the table is modified. If ONLY is not specified, the table and all subtables will be modified. You can add the asterisk (*) option following the table name to specify that all subtables are scanned, which is the default operation.

• constraint_name

  Specifies the name of an existing constraint to drop.

• index_name

  Specifies the name of this index.

• storage_parameter

  Specifies the name of a storage parameter.

• new_owner

  Specifies the name of the new table owner.

• new_tablespace

  Specifies the new name of the tablespace to which the table belongs.

• column_name, column_1_name, column_2_name

  Specifies the name of a new or an existing column.

• data_type

  Specifies the type of a new column or a new type of an existing column.

• compress_mode

  Specifies the compress options of the table, only available for row-based tables. The clause specifies the algorithm preferentially used by the column.

• collation

  Specifies the collation rule name of a column. The optional COLLATE clause specifies a collation for the new column; if omitted, the collation is the default for the new column.

• USING expression

  A USING clause specifies how to compute the new column value from the old; if omitted, the default conversion is an assignment cast from old data type to new. A USING clause must be provided if there is no implicit or assignment cast from the old to new type.

  

  USING in ALTER TYPE can specify any expression involving the old values of the row; that is, it can refer to any columns other than the one being converted. This allows very general conversions to be done with the ALTER TYPE syntax. Because of this flexibility, the USING expression is not applied to the column's default value (if any); the result might not be a constant expression as required for a default. This means that when there is no implicit or assignment cast from old to new type, ALTER TYPE might fail to convert the default even though a USING clause is supplied. In such cases, drop the default with DROP DEFAULT, perform the ALTER TYPE, and then use SET DEFAULT to add a suitable new default. Similar considerations apply to indexes and constraints involving the column.

• NOT NULL | NULL

  Sets whether the column allows null values.

• integer

  Specifies the constant value of an integer with a sign. If PERCENT is used, the range of integer is from 0 to 100.

• attribute_option

  Specifies an attribute option.

• PLAIN | EXTERNAL | EXTENDED | MAIN

  Specifies a column storage mode.

  • PLAIN must be used for fixed-length values (such as integers). It must be inline and uncompressed.
  • MAIN is for inline, compressible data.
  • EXTERNAL is for external, uncompressed data. Use of EXTERNAL will make substring operations on text and bytea values run faster, at the penalty of increased storage space.
  • EXTENDED is for external, compressed data. EXTENDED is the default for most data types that support non-PLAIN storage.
• CHECK ( expression )

  New or updated rows must satisfy for an insert or update operation to succeed. Expressions evaluating to TRUE succeed. If any row of an insert or update operation produces a FALSE result, an error exception is raised and the insert or update does not alter the database.

  A check constraint specified as a column constraint should reference only the column's values, while an expression appearing in a table constraint can reference multiple columns.

  Currently, CHECK expression does not include subqueries and cannot use variables apart from the current column.

• DEFAULT default_expr

  Assigns a default data value for a column.

  The data type of the default expression must match the data type of the column.

  The default expression will be used in any insert operation that does not specify a value for the column. If there is no default value for a column, then the default value is NULL.

• UNIQUE index_parameters

  UNIQUE ( column_name [, ... ] ) index_parameters

  The UNIQUE constraint specifies that a group of one or more columns of a table can contain only unique values.

• PRIMARY KEY index_parameters

  PRIMARY KEY ( column_name [, ... ] ) index_parameters

  The primary key constraint specifies that a column or columns of a table can contain only unique (non-duplicate) and non-null values.

• DEFERRABLE | NOT DEFERRABLE | INITIALLY DEFERRED | INITIALLY IMMEDIATE

  Sets whether the constraint is deferrable. This option is unavailable to column-store tables.

  • DEFERRABLE: deferrable can be postponed until the end of the transaction using the SET CONSTRAINTS command.
  • NOT DEFERRABLE: checks immediately after the execution of each command.
  • INITIALLY IMMEDIATE: checks immediately after the execution of each statement.
  • INITIALLY DEFERRED: checks when the transaction ends.
• WITH ( {storage_parameter = value} [, ... ] )

  Specifies an optional storage parameter for a table or an index.

• COMPRESS|NOCOMPRESS
  • NOCOMPRESS: If the NOCOMPRESS keyword is specified, the existing compression feature of the table is not changed.
  • COMPRESS: If the COMPRESS keyword is specified, the table compression feature is triggered if tuples are inserted in a batch.
• new_table_name

  Specifies the new table name.

• new_column_name

  Specifies the new name of a specific column in a table.

• new_constraint_name

  Specifies the new name of a table constraint.

• new_schema

  Specifies the new schema name.

• CASCADE

  Automatically drops objects that depend on the dropped column or constraint (for example, views referencing the column).

• RESTRICT

  Refuses to drop the column or constraint if there are any dependent objects. This is the default behavior.

• schema_name

  Specifies the schema name of a table.

Examples

Create an index ds_warehouse_t1_index1 for the table tpcds.warehouse_t1. Then add primary key constraints, and rename the created index.

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CREATE UNIQUE INDEX ds_warehouse_t1_index1 ON tpcds.warehouse_t1(W_WAREHOUSE_SK);
ALTER TABLE tpcds.warehouse_t1 ADD CONSTRAINT ds_warehouse_t1_index2 PRIMARY KEY USING INDEX ds_warehouse_t1_index1;

Delete the primary key ds_warehouse_t1_index2 from the table tpcds.warehouse_t1.

1

ALTER TABLE warehouse_t1 DROP CONSTRAINT ds_warehouse_t1_index2;

Add a varchar column to the tpcds.warehouse_t19 table.

1

ALTER TABLE tpcds.warehouse_t19 ADD W_GOODS_CATEGORY varchar(30);

Add a check constraint to the tpcds.warehouse_t19 table.

1

ALTER TABLE tpcds.warehouse_t19 ADD CONSTRAINT W_CONSTR_KEY4 CHECK (W_STATE <> '');

Use one statement to alter the types of two existing columns.

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ALTER TABLE tpcds.warehouse_t19
ALTER COLUMN W_GOODS_CATEGORY TYPE varchar(80),
ALTER COLUMN W_STREET_NAME TYPE varchar(100);

This statement is equivalent to the preceding statement.

1

ALTER TABLE tpcds.warehouse_t19 MODIFY (W_GOODS_CATEGORY varchar(30), W_STREET_NAME varchar(60));

Add a Not-Null constraint to an existing column.

1

ALTER TABLE tpcds.warehouse_t19 ALTER COLUMN W_GOODS_CATEGORY SET NOT NULL;

Remove Not-Null constraints from an existing column.

1

ALTER TABLE tpcds.warehouse_t19 ALTER COLUMN W_GOODS_CATEGORY DROP NOT NULL;

If no partial clusters have been specified in a column-store table, add a partial cluster to the table.

1

ALTER TABLE tpcds.warehouse_t17 ADD PARTIAL CLUSTER KEY(W_WAREHOUSE_SK);

View a constraint name.

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\d+ tpcds.warehouse_t17
                              Table "tpcds.warehouse_t17"
      Column       |         Type          | Modifiers | Storage  | Stats target | Description 
-------------------+-----------------------+-----------+----------+--------------+-------------
 w_warehouse_sk    | integer               | not null  | plain    |              | 
 w_warehouse_id    | character(16)         | not null  | extended |              | 
 w_warehouse_name  | character varying(20) |           | extended |              | 
 w_warehouse_sq_ft | integer               |           | plain    |              | 
 w_street_number   | character(10)         |           | extended |              | 
 w_street_name     | character varying(60) |           | extended |              | 
 w_street_type     | character(15)         |           | extended |              | 
 w_suite_number    | character(10)         |           | extended |              | 
 w_city            | character varying(60) |           | extended |              | 
 w_county          | character varying(30) |           | extended |              | 
 w_state           | character(2)          |           | extended |              | 
 w_zip             | character(10)         |           | extended |              | 
 w_country         | character varying(20) |           | extended |              | 
 w_gmt_offset      | numeric(5,2)          |           | main     |              | 
Partial Cluster :
    "warehouse_t17_cluster" PARTIAL CLUSTER KEY (w_warehouse_sk)
Has OIDs: no
Distribute By: HASH(w_warehouse_sk)
Location Nodes: ALL DATANODES
Options: orientation=column, compression=high, colversion=2.0, enable_delta=false

Delete a partial cluster column from the column-store table.

1

ALTER TABLE tpcds.warehouse_t17 DROP CONSTRAINT warehouse_t17_cluster;

Create the joe schema.

1

CREATE SCHEMA joe;

Move a table to another schema.

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ALTER TABLE tpcds.warehouse_t19 SET SCHEMA joe;

Rename an existing table.

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ALTER TABLE joe.warehouse_t19 RENAME TO joe.warehouse_t23;

Change the distribution mode of the tpcds.warehouse_t22 table to REPLICATION.

1

ALTER TABLE tpcds.warehouse_t22 DISTRIBUTE BY REPLICATION;

Change the distribution column of the tpcds.warehouse_t22 table to W_WAREHOUSE_SK.

1

ALTER TABLE tpcds.warehouse_t22 DISTRIBUTE BY HASH(W_WAREHOUSE_SK);

Delete a column from the warehouse_t23 table.

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ALTER TABLE joe.warehouse_t23 DROP COLUMN W_STREET_NAME;

Switch the storage format of a column-store table.

1

ALTER TABLE tpcds.warehouse_t26 SET (COLVERSION = 1.0);

Disable the delta table function of the column-store table.

1

ALTER TABLE tpcds.warehouse_t27 SET (ENABLE_DELTA = OFF);

Disable the SKIP_FPI_HINT function of the table.

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ALTER TABLE tpcds.warehouse_t29 SET (SKIP_FPI_HINT = FALSE);

Change the data temperature for a single table.

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ALTER TABLE tpcds.warehouse_t28 REFRESH STORAGE;

Change the data temperature for multiple tables in batches.

SELECT pg_refresh_storage();

Links

CREATE TABLE, DROP TABLE