the problem is Update the salary of all the employees by 50% who had worked on 5 or more than 5 projects, by 30% (= 3 projects), by 20 % (= 1 projects) the number of project is got by performing a group by query on the EMPLOYEE_PROJECT_HISTORY; i have tried these queries 1) update emp set emp.sal= case when jemp.pcount >=5 then emp.sal+ (emp.sal*50)/100 when jemp.pcount >=3 then emp.sal+ (emp.sal*30)/100 when jemp.pcount >=1 then emp.sal+ (emp.sal*20)/100 else emp.sal+ (emp.sal*20)/100 end from employee emp join (select empno as jempno,count(projectno) as pcount from EMPLOYEE_PROJECT_HISTORY by empno) jemp on emp.empno=jemp.jempno ; 2)update employee a set a.sal= case (select count(b.projectno) as pcount from EMPLOYEE_PROJECT_HISTORY b group by b.empno ) when b.pcount >5 then a.sal = a.sal+ (a.sal*50)/100 when pcount >3 then a.sal = a.sal+ (a.sal*30)/100 when pcount >1 then a.sal = a.sal+ (a.sal*20)/100 end;