--------DATA in Cat_Tbl---------------------------
Cat1           Cat2          Value
a              e1            113
b              e1            14
a              e2            15
c              e3            13
a              e1            13
a              e2            11
c              e4            1

PROBLEM:

For each distinct value in Cat1, user wants to find maximum of Values grouped by Cat2 and then sum them up. 

Step 1: User wants to extract the following rows for example where Cat1 = ‘a’.

Cat1 Cat2 Value 
a    e1   113 
a    e2   15 
a    e1   13 
a    e2   11

Step 2: User wants to extract maximum corresponding to Cat1 and Cat2:

Cat1 Cat2 Value 
a    e1   113 
a    e2   15

Step 3: User wants to sum the Values for Cat1.

Cat1 SumOfValueColumn 
a    128 
b    14 
c    14

SOLUTION 1 USING TEMPORARY TABLE #Max_Cat_Tbl

select Cat1, Cat2, max(Value) Maxvalue 
into #Max_Cat_Tbl from Cat_Tbl 
group by Cat1, Cat2 order by 1, 2 
select Cat1, sum(Maxvalue) 
from #Max_Cat_Tbl 
group by Cat1 
order by Cat1 
drop table #Max_Cat_Tbl 
go

SOLUTION 2 USING VIEW Max_Cat_Tbl_View

create view Max_Cat_Tbl_View 
( Cat1, Cat2, Maxvalue ) as 
select Cat1, Cat2, max(Value) 
from Cat_Tbl 
group by Cat1, Cat2 
select Cat1, sum(Maxvalue) 
from Max_Cat_Tbl_View 
group by Cat1 
order by Cat1 
go

Good SQL, good night.