with orders as (
select 1 ord_id, 'Order 1' ord_name from dual union all
select 2 ord_id, 'Order 2' ord_name from dual union all
select 3 ord_id, 'Order 3' ord_name from dual
)
, order_lines as (
select 1 ord_id, 1 line_id, 'O1 L1' line_name from dual union all
select 1 ord_id, 2 line_id, 'O1 L2' line_name from dual union all
select 2 ord_id, 3 line_id, 'O2 L1' line_name from dual union all
select 2 ord_id, 4 line_id, 'O2 L2' line_name from dual union all
select 2 ord_id, 5 line_id, 'O2 L3' line_name from dual union all
select 3 ord_id, 6 line_id, 'O3 L1' line_name from dual
)
select ord_id, ord_name, line_name 
from (  select o.ord_id, 
               o.ord_name, 
               ol.line_name, 
               row_number() over (partition by o.ord_id order by line_id) rn
        from orders o
         inner join order_lines ol on o.ord_id = ol.ord_id)
where rn = 1