Consider the following relational schema: Emp(eid:integer, ename:string, age:integer, salary:real) where the key is: eid:integer

The underlined attributes are keys for their relations. Consider the following SQL query:

Select * From Emp Where age = 20 and salary > 20000 

Describe the index on Emp that improves the running time of this query more than every other index over most Emp relation instances. Explain the attributes, their order, type (B+ tree or hash) of the index and whether it should be clustered.