Description

ALTER TYPE changes the definition of an existing type. There are several subforms:

The ADD ATTRIBUTE, DROP ATTRIBUTE, and ALTER ATTRIBUTE actions can be combined into a list of multiple alterations to apply in parallel. For example, it is possible to add several attributes and/or alter the type of several attributes in a single command.

You must own the type to use ALTER TYPE. To change the schema of a type, you must also have CREATE privilege on the new schema. To alter the owner, you must be able to SET ROLE to the new owning role, and that role must have CREATE privilege on the type's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the type. However, a superuser can alter ownership of any type anyway.) To add an attribute or alter an attribute type, you must also have USAGE privilege on the attribute's data type.

Parameters

Notes

If ALTER TYPE ... ADD VALUE (the form that adds a new value to an enum type) is executed inside a transaction block, the new value cannot be used until after the transaction has been committed.

Comparisons involving an added enum value will sometimes be slower than comparisons involving only original members of the enum type. This will usually only occur if BEFORE or AFTER is used to set the new value's sort position somewhere other than at the end of the list. However, sometimes it will happen even though the new value is added at the end (this occurs if the OID counter “wrapped around” since the original creation of the enum type). The slowdown is usually insignificant; but if it matters, optimal performance can be regained by dropping and recreating the enum type, or by dumping and restoring the database.

Examples

To rename a data type:

ALTER TYPE electronic_mail RENAME TO email;

To change the owner of the type email to joe:

ALTER TYPE email OWNER TO joe;

To change the schema of the type email to customers:

ALTER TYPE email SET SCHEMA customers;

To add a new attribute to a composite type:

ALTER TYPE compfoo ADD ATTRIBUTE f3 int;

To add a new value to an enum type in a particular sort position:

ALTER TYPE colors ADD VALUE 'orange' AFTER 'red';

To rename an enum value:

ALTER TYPE colors RENAME VALUE 'purple' TO 'mauve';

To create binary I/O functions for an existing base type:

CREATE FUNCTION mytypesend(mytype) RETURNS bytea ...;
CREATE FUNCTION mytyperecv(internal, oid, integer) RETURNS mytype ...;
ALTER TYPE mytype SET (
    SEND = mytypesend,
    RECEIVE = mytyperecv
);

Compatibility

The variants to add and drop attributes are part of the SQL standard; the other variants are PostgreSQL extensions.

See Also