Another solution:
DECLARE @shiftno INT
SELECT @shiftno=MAX([shiftno])
FROM Table1
SELECT SUM([amount]) AS SumOfAmount
FROM Table1
WHERE [shiftno]=@shiftno
It should works too:
SELECT SUM([amount]) AS SumOfAmount
FROM Table1
HAVING 1=MAX([shiftno])
To get the sum of amount for each shiftno:
SELECT [shiftno], SUM([amount]) AS SumOfAmount
FROM Table1
GROUP BY [shiftno]