How to join 2 queries with different number of records and columns in oracle sql?

Question

I have three tables:

Employee_leave(EmployeeID,Time_Period,leave_type)  
Employee(EID,Department,Designation) 
 leave_eligibility(Department,Designation, LeaveTy         


        

Answer 1

To get the final desired output ...

"For a record which is not present in output of query1, it should display 0 in final output. "

... use an outer join to tie the taken leave records to the other tables. This will give zero time_duration for leave types which the employee has not taken.

select emp.Employee_ID
       , le.leavetype
       , le.leavebalance 
       , sum (el.Time_Duration) as total_Time_Duration
from employee emp
     inner join leave_eligibility le
          on le.department= emp.department 
             and le.designation= emp.designation 
     left outer join Employee_leave el
           on el.EmployeeID = emp.Employee_ID
           and el.leave_type = le.leavetype        
group by emp.Employee_ID
       , le.leavetype
       , le.leavebalance 
       ;

Your immediate problem:

I'm getting "%s: invalid identifier"

Your view has references to a column EID although none of your posted tables have a column of that name. Likewise there is confusion between Time_Duration and time_period.

More generally, you will find life considerably easier if you use the exact same name for common columns (i.e. consistently use either employee_id or employeeid, don't chop and change).