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.

Precautions

  • Avoid performing ALTER TABLE, ALTER TABLE PARTITION, DROP PARTITION, and TRUNCATE operations during peak hours to prevent long SQL statements from blocking these operations or SQL services.
  • For more information about development and design specifications, see "GaussDB(DWS) Development and Design Proposal" in the GaussDB(DWS) Developer Guide.

Syntax

Parameter Description

Table Operation Examples

Rename a table:

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ALTER TABLE CUSTOMER RENAME TO CUSTOMER_t;

Add a new table constraint:

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ALTER TABLE customer_address ADD PRIMARY KEY(ca_address_sk);

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

Create an index CUSTOMER_constraint1 for the table CUSTOMER. Then add primary key constraints, and rename the created index.

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CREATE UNIQUE INDEX CUSTOMER_constraint1 ON CUSTOMER(C_CUSTKEY);
ALTER TABLE CUSTOMER ADD CONSTRAINT CUSTOMER_constraint2 PRIMARY KEY USING INDEX CUSTOMER_constraint1;

Rename a table constraint:

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ALTER TABLE CUSTOMER RENAME CONSTRAINT CUSTOMER_constraint2 TO CUSTOMER_constraint;

Delete a table constraint:

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ALTER TABLE CUSTOMER DROP CONSTRAINT CUSTOMER_constraint;

Add a table index:

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ALTER TABLE CUSTOMER ADD INDEX CUSTOMER_index(C_CUSTKEY);

Delete a table index:

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ALTER TABLE CUSTOMER DROP INDEX CUSTOMER_index;
ALTER TABLE CUSTOMER DROP KEY CUSTOMER_index;

Add a partial cluster key to a column-store table:

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ALTER TABLE customer_address ADD CONSTRAINT customer_address_cluster PARTIAL CLUSTER KEY(ca_address_sk);

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

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ALTER TABLE customer_address DROP CONSTRAINT customer_address_cluster;

Switch the storage format of a column-store table:

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ALTER TABLE customer_address SET (COLVERSION = 1.0);

Change the distribution mode of a table:

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ALTER TABLE customer_address DISTRIBUTE BY REPLICATION;

Change the schema of a table:

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ALTER TABLE customer_address SET SCHEMA tpcds;

Change the data temperature for a single table:

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ALTER TABLE cold_hot_table REFRESH STORAGE;

Change a column-store partitioned table to a table that supports hot and cold data separation.

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CREATE table test_1(id int,d_time date)
WITH(ORIENTATION=COLUMN)
DISTRIBUTE BY HASH (id)
PARTITION BY RANGE (d_time)
(PARTITION p1 START('2022-01-01') END('2022-01-31') EVERY(interval '1 day'))

ALTER TABLE test_1 SET (storage_policy = 'LMT:100');

Modify the table cache policy (supported only in clusters of the storage-compute decoupling 3.0 version).

ALTER TABLE orders SET (cache_policy = 'NONE');

Column Operation Examples

Add a column to a table.

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ALTER TABLE warehouse_t ADD W_GOODS_CATEGORY int;

Modify the column name and column field information in the table.

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ALTER TABLE warehouse_t CHANGE W_GOODS_CATEGORY W_GOODS_CATEGORY2 DECIMAL NOT NULL COMMENT 'W_GOODS_CATEGORY';

Add a primary key to a table.

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ALTER TABLE warehouse_t ADD PRIMARY KEY(w_warehouse_name);

Rename a column.

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ALTER TABLE CUSTOMER RENAME C_PHONE TO new_C_PHONE;

Add columns to a table.

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ALTER TABLE CUSTOMER ADD (C_COMMENT VARCHAR(117) NOT NULL, C_COUNT int);

Change the data type of a column in the table and set the column constraint to NOT NULL.

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ALTER TABLE CUSTOMER MODIFY C_MKTSEGMENT varchar(20) NOT NULL;

Add the NOT NULL constraint to a column in the table.

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ALTER TABLE CUSTOMER ALTER COLUMN C_PHONE SET NOT NULL;

Delete a column from a table.

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ALTER TABLE CUSTOMER DROP COLUMN C_COUNT;

Add an index to a column in the table.

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ALTER TABLE customer_address MODIFY ca_address_id varchar(20) CONSTRAINT ca_address_index CHECK (ca_address_id > 0);

Add a timestamp column with the ON UPDATE expression to the customer_address table.

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ALTER TABLE customer_address ADD COLUMN C_TIME timestamp on update current_timestamp;

Delete the timestamp column with the ON UPDATE expression from the customer_address.

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ALTER TABLE customer_address MODIFY COLUMN C_TIME timestamp on update NULL;

Helpful Links

CREATE TABLE, 12.101-RENAME TABLE, and DROP TABLE

Parent topic: DDL Syntax