DataSource Controls :: How Get Sum Of Different Pairs

The table design is like this:

ColumnA -- varchar(50)
ColumnB -- varchar (50)
ColumnC -- int
The table data is like this:
ColumnA ColumnB ColumnC
Abc def 10
Abc pqr 10
Abc def 20
Def pqr 50

The required output is:

Abc def 30
Abc pqr 10
Def pqr 10

That is if the records of the different rows of ColumnA & ColumnB are same then sumation of ColumnC should be done. Otherwise data is displayed as it is.