with unique_start as (
    select a.start_date
    from projects A
        left join projects t
        on a.start_date = t.end_date
    where t.end_date is null
),
unique_end as (
    select a.end_date
    from projects A
        left join projects t
        on a.end_date = t.start_date
    where t.start_date is null
)
select start_date, min(end_date) 
from unique_start join unique_end on start_date < end_date
group by start_date
order by datediff(day, start_date, min(end_date)), start_date