with cte1 as(
    select start_date,
    row_number() over (order by start_date) as rn1
    from projects
    where start_date not in(
    select end_date from projects)
)
,cte2 as(
    select end_date,
    row_number() over (order by start_date) as rn2
    from projects
    where end_date not in( 
    select start_date from projects)
    
)
select cte1.start_date,cte2.end_date from cte1,cte2
where rn1=rn2
order by datediff(day,cte1.start_date,cte2.end_date) asc, cte1.start_date;