Employee    Role    Contract Hours  IS primary Role Valid from
1   Role A  35  Y   01/03/2015
1   Role B  35  Y   01/06/2016
1   Role C  0   N   01/07/2016
2   Role A  20  Y   01/01/2016
2   Role B  0   N   01/01/2016
2   Role C  25  Y   01/04/2016
3   Role A  35  Y   01/04/2016

Employee    Role    Contract Hours  Valid from  Primary Role – Contract Hours
1   Role A  35  01/03/2015  Role A – 35
1   Role B  35  01/06/2016  Role B – 35
1   Role C  0   01/07/2016  Role B – 35
2   Role A  20  01/01/2016  Role A – 20
2   Role B  0   01/01/2016  Role A – 20
2   Role C  25  01/04/2016  Role C – 25
3   Role A  35  01/04/2016  Role A – 35

Select
“Employee”,
“Role”,
“Contract Hours”,
“Valid From”,
 Case
When “Is primary Role” = Y
Then “Role” + ‘-‘ + “Contract Hours”
    Else NULL
 END as “Primary Role – Contract Hours”