RealPage interview faced questions

1. Group by rollup
2.Difference between having vs where
3.union vs union all
4. Split string to table
5.Migration approach
6.Query tuning
7.Sql query execution plan
8.pivot vs unpivot example:

one table have columns with CustomerId,Year,Jan,feb,march,apr,may,june,july,aug,sep,oct,nov,dec,CustomerBalance
then we need table like customerid,year,Month,CustomerBalance