variable_declaration ::=
   variable_name datatype [ [ NOT NULL] {:= | DEFAULT} expression ] ;

datatype ::=
   { collection_name %TYPE
   | collection_type_name
   | cursor_name %ROWTYPE>
   | cursor_variable_name %TYPE
   | db_table_name { %ROWTYPE | .column_name %TYPE }
   | object_name %TYPE
   | [REF] object_type_name
   | record_name %TYPE
   | record_type_name
   | ref_cursor_type_name
   | scalar_datatype_name
   | variable_name %TYPE
   }