# ALTER TABLE#

## Synopsis#

ALTER TABLE [ IF EXISTS ] name RENAME TO new_name
ALTER TABLE [ IF EXISTS ] name ADD COLUMN [ IF NOT EXISTS ] column_name data_type
[ NOT NULL ] [ COMMENT comment ]
[ WITH ( property_name = expression [, ...] ) ]
ALTER TABLE [ IF EXISTS ] name DROP COLUMN [ IF EXISTS ] column_name
ALTER TABLE [ IF EXISTS ] name RENAME COLUMN [ IF EXISTS ] old_name TO new_name
ALTER TABLE name SET AUTHORIZATION ( user | USER user | ROLE role )
ALTER TABLE name SET PROPERTIES property_name = expression [, ...]
ALTER TABLE name EXECUTE command [ ( parameter => expression [, ... ] ) ]
[ WHERE expression ]


## Description#

Change the definition of an existing table.

The optional IF EXISTS (when used before the table name) clause causes the error to be suppressed if the table does not exists.

The optional IF EXISTS (when used before the column name) clause causes the error to be suppressed if the column does not exists.

The optional IF NOT EXISTS clause causes the error to be suppressed if the column already exists.

### SET PROPERTIES#

The ALTER TABLE SET PROPERTIES statement followed by some number of property_name and expression pairs applies the specified properties and values to a table. Ommitting an already-set property from this statement leaves that property unchanged in the table.

A property in a SET PROPERTIES statement can be set to DEFAULT, which reverts its value back to the default in that table.

Support for ALTER TABLE SET PROPERTIES varies between connectors, as not all connectors support modifying table properties.

### EXECUTE#

The ALTER TABLE EXECUTE statement followed by a command and parameters modifies the table according to the specified command and parameters. ALTER TABLE EXECUTE supports different commands on a per-connector basis.

You can use the => operator for passing named parameter values. The left side is the name of the parameter, the right side is the value being passed:

ALTER TABLE hive.schema.test_table EXECUTE optimize(file_size_threshold => '10MB')


## Examples#

Rename table users to people:

ALTER TABLE users RENAME TO people;


Rename table users to people if table users exists:

ALTER TABLE IF EXISTS users RENAME TO people;


Add column zip to the users table:

ALTER TABLE users ADD COLUMN zip varchar;


Add column zip to the users table if table users exists and column zip not already exists:

ALTER TABLE IF EXISTS users ADD COLUMN IF NOT EXISTS zip varchar;


Drop column zip from the users table:

ALTER TABLE users DROP COLUMN zip;


Drop column zip from the users table if table users and column zip exists:

ALTER TABLE IF EXISTS users DROP COLUMN IF EXISTS zip;


Rename column id to user_id in the users table:

ALTER TABLE users RENAME COLUMN id TO user_id;


Rename column id to user_id in the users table if table users and column id exists:

ALTER TABLE IF EXISTS users RENAME column IF EXISTS id to user_id;


Change owner of table people to user alice:

ALTER TABLE people SET AUTHORIZATION alice


Allow everyone with role public to drop and alter table people:

ALTER TABLE people SET AUTHORIZATION ROLE PUBLIC


Set table properties (x = y) in table people:

ALTER TABLE people SET PROPERTIES x = 'y';


Set multiple table properties (foo = 123 and foo bar = 456) in table people:

ALTER TABLE people SET PROPERTIES foo = 123, "foo bar" = 456;


Set table property x to its default value in tablepeople:

ALTER TABLE people SET PROPERTIES x = DEFAULT;


Collapse files in a table that are over 10 megabytes in size, as supported by the Hive connector:

ALTER TABLE hive.schema.test_table EXECUTE optimize(file_size_threshold => '10MB')