DROP USER
DROP USER username
[CASCADE]
The DBA’s favorite command, this statement removes a user (username) from the database.
You must have the DROP USER privilege to remove a user from the database. Note that if you specify the CASCADE option, any referential integrity constraints on tables in other schemas that refer to primary and unique keys on tables in this schema will also be dropped. If tables or other database objects in this schema are referred to by views, synonyms, or stored procedures, functions, or packages in another schema, those referring objects will be marked invalid but not dropped.