select_statement: 'SELECT' opt_distinct fields_list 'FROM' tables_list opt_where opt_orderby opt_groupby
    ;

opt_distinct: 'DISTINCT' | ;

opt_where: 'WHERE' where_list | ;

fields_list: field
     | field ',' fields_list
     ;

opt_groupby: 'GROUP BY' fields_list | ;

opt_orderby: 'ORDER BY' order_fields_list | ;

order_fields_list: order_field
     | order_field ',' order_fields_list 
     ;