Find the startdate and enddate for Gold Rate?

If the gold rate is changed then only we have to create a new row.

Input:

Output:

Try this code

;with table as
(
Select '2018-01-18' DateColumn, 100 value union
Select '2018-01-19' DateColumn, 100 value union
Select '2018-01-20' DateColumn, 300 value union
Select '2018-01-21' DateColumn, 400 value
), cte as
(
Select *, ROW_NUMBER() over (Partition By Value Order By DateColumn) idx from table
)
Select a.DateColumn FirstDate, case when b.DateColumn is null then a.DateColumn else b.DateColumn end SecondDate, a.value
from cte a
left join (select * from cte where idx = 2) b
on a.value = b.value
Where a.idx = 1