Database: planet_1
Question: Find the number of employees who do not have clearance in Mars .
SQL:
select count(*) from employee where employeeid not in ( select t2.employeeid from has_clearance as t1 join employee as t2 on t1.employee = t2.employeeid join planet as t3 on t1.planet = t3.planetid where t3.name = "mars" );