Breck Carter has several times posted a procedure for dropping all connections to a database. 
Here is a modified version of that procedure. 
It is useful when you need to have exclusive access to a database.

-- How to get full control over an ASA server...
--    call sa_server_option ( 'disable_connections', 'ON' );
--    call sa_drop_other_connections(); 
--       ...do your thing
--    call sa_server_option ( 'disable_connections', 'OFF' )

-- Attempts to connect will get "ASA Error -99: 
--    Connections to database have been disabled".

call sa_make_object( 'procedure', 'sa_drop_other_connections', 'dbo' );

ALTER PROCEDURE dbo.sa_drop_other_connections ()

BEGIN 

DECLARE @this_connection_id    INTEGER;
DECLARE @other_connection_id   INTEGER;
DECLARE @conn_ident VARCHAR(200);
DECLARE @node_address VARCHAR(100);

SET @this_connection_id =  connection_property ( 'number' );
SET @other_connection_id = NEXT_CONNECTION ( NULL );

WHILE @other_connection_id IS NOT NULL LOOP

  SET @node_address = connection_property ( 'NodeAddress', @other_connection_id );
  SET @conn_ident = STRING( 
         connection_property ( 'Userid', @other_connection_id ), '-',
         IF COALESCE ( @node_address, '' ) <> ''
            THEN STRING ( @node_address, ' - ' )
            ELSE ''
         ENDIF,
         @other_connection_id );

   IF @other_connection_id = @this_connection_id THEN
      MESSAGE 'Not dropping this connection: ' || @conn_ident TO CLIENT;
   ELSE 
      MESSAGE 'Dropping other connection: ' || @conn_ident TO CLIENT;
      EXECUTE IMMEDIATE 'DROP CONNECTION ' || @other_connection_id;
   END IF;

   SET @other_connection_id = NEXT_CONNECTION ( @other_connection_id );

END LOOP;

END;