DROP INDEX

Description

drops an existing index from the database system. To execute this command you must be the owner of the index.

IF EXISTS

Do not throw an error if the index does not exist. A notice is issued in this case.

The name (optionally schema-qualified) of an existing index.

CASCADE

Automatically drop objects that depend on the index.

Refuse to drop the index if any objects depend on it. This is the default.

Remove the index :

is a Greenplum Database language extension. There are no provisions for indexes in the SQL standard.