DROP DATABASE — remove a database
DROP DATABASE [ IF EXISTS ] name
   DROP DATABASE drops a database. It removes the
   catalog entries for the database and deletes the directory
   containing the data.  It can only be executed by the database owner.
   Also, it cannot be executed while you or anyone else are connected
   to the target database.  (Connect to postgres or any
   other database to issue this command.)
  
   DROP DATABASE cannot be undone.  Use it with care!
  
IF EXISTSDo not throw an error if the database does not exist. A notice is issued in this case.
nameThe name of the database to remove.
    DROP DATABASE cannot be executed inside a transaction
    block.
   
This command cannot be executed while connected to the target database. Thus, it might be more convenient to use the program dropdb instead, which is a wrapper around this command.
   There is no DROP DATABASE statement in the SQL standard.