Alter Table

Alter Table Statement

ALTER TABLE - changes the schema of an existing table in the catalog.

Examples

-- add a new column with name "k" to the table "integers", it will be filled with the default value NULL
ALTER TABLE integers ADD COLUMN k INTEGER;
-- add a new column with name "l" to the table integers, it will be filled with the default value 10
ALTER TABLE integers ADD COLUMN l INTEGER DEFAULT 10;

-- drop the column "k" from the table integers
ALTER TABLE integers DROP k;

-- change the type of the column "i" to the type "VARCHAR" using a standard cast
ALTER TABLE integers ALTER i TYPE VARCHAR;
-- change the type of the column "i" to the type "VARCHAR", using the specified expression to convert the data for each row
ALTER TABLE integers ALTER i SET DATA TYPE VARCHAR USING CONCAT(i, '_', j);

-- set the default value of a column
ALTER TABLE integers ALTER COLUMN i SET DEFAULT 10;
-- drop the default value of a column
ALTER TABLE integers ALTER COLUMN i DROP DEFAULT;

-- rename a table
ALTER TABLE integers RENAME TO integers_old;

-- rename a column of a table
ALTER TABLE integers RENAME i TO j;

Syntax

ALTER TABLE changes the schema of an existing table. All the changes made by ALTER TABLE fully respect the transactional semantics - that is - they will not be visible to other transactions until committed, and can be fully reverted through a rollback.

RENAME TABLE

-- rename a table
ALTER TABLE integers RENAME TO integers_old;

The RENAME TO clause renames an entire table, changing its name in the schema. Note that any views that rely on the table are not automatically updated.

RENAME COLUMN

-- rename a column of a table
ALTER TABLE integers RENAME i TO j;
ALTER TABLE integers RENAME COLUMN j TO k;

The RENAME COLUMN clause renames a single column within a table. Any constraints that rely on this name (e.g. CHECK constraints) are automatically updated. However, note that any views that rely on this column name are not automatically updated.

ADD COLUMN

-- add a new column with name "k" to the table "integers", it will be filled with the default value NULL
ALTER TABLE integers ADD COLUMN k INTEGER;
-- add a new column with name "l" to the table integers, it will be filled with the default value 10
ALTER TABLE integers ADD COLUMN l INTEGER DEFAULT 10;

The ADD COLUMN clause can be used to add a new column of a specified type to a table. The new column will be filled with the specified default value, or NULL if none is specified.

DROP COLUMN

-- drop the column "k" from the table integers
ALTER TABLE integers DROP k;

The DROP COLUMN clause can be used to remove a column from a table. Note that columns can only be removed if they do not have any indexes that rely on them. This includes any indexes created as part of a PRIMARY KEY or UNIQUE constraint. Columns that are part of multi-column check constraints cannot be dropped either.

ALTER TYPE

-- change the type of the column "i" to the type "VARCHAR" using a standard cast
ALTER TABLE integers ALTER i TYPE VARCHAR;
-- change the type of the column "i" to the type "VARCHAR", using the specified expression to convert the data for each row
ALTER TABLE integers ALTER i SET DATA TYPE VARCHAR USING CONCAT(i, '_', j);

The SET DATA TYPE clause changes the type of a column in a table. Any data present in the column is converted according to the provided expression in the USING clause, or, if the USING clause is absent, cast to the new data type. Note that columns can only have their type changed if they do not have any indexes that rely on them and are not part of any CHECK constraints.

SET/DROP DEFAULT

-- set the default value of a column
ALTER TABLE integers ALTER COLUMN i SET DEFAULT 10;
-- drop the default value of a column
ALTER TABLE integers ALTER COLUMN i DROP DEFAULT;

The SET/DROP DEFAULT clause modifies the DEFAULT value of an existing column. Note that this does not modify any existing data in the column. Dropping the default is equivalent to setting the default value to NULL.