show the names of all scientists.
select name from scientists
find the ssn of scientists named Michael Rogers and Carol Smith.
select ssn from scientists where name = 'Michael Rogers' or name = 'Carol Smith'
what are the names of projects that they are assigned to?
select t2.name from assignedto as t1 join projects as t2 on t1.project = t2.code join scientists as t3 on t1.scientist = t3.ssn where t3.name = 'Michael Rogers' or t3.name = 'Carol Smith'
how many hours in total have been spent on these projects?
select sum(t2.hours) from assignedto as t1 join projects as t2 on t1.project = t2.code join scientists as t3 on t1.scientist = t3.ssn where t3.name = 'Michael Rogers' or t3.name = 'Carol Smith'