Answer: 
		
let's us assume that we have the following table of Employee.
 
| Emp_Id | Emp_Name | Emp_Salary_2010 | Emp_Salary_2011 | 
| 1 
 | Shiv | 17000 | 19000 | 
| 2 
 | Raju 
 | 13500 | 15000 | 
| 3 
 | Sham | 15000 | 18000 | 
| 4 
 | Moosa | 11000 | 14000 | 
| 5 
 | Feroz | 12000 | 16000 | 
                      
Now we want to merge the Emp_Salary_2010 and Emp_Salary_2011 columns into a 
single column as Salary. 
Query:-
 select Emp_Name,Emp_Salary_2010 as Salary from Employee
union  
select Emp_Name,Emp_Salary_2011 as Salary from Employee
Output:-
 | Emp_Name | Salary | 
| Shiv | 17000 | 
| Shiv | 19000 | 
| Raju 
 | 13500 | 
| Raju 
 | 15000 | 
| Sham 
 | 15000 | 
| Sham 
 | 18000 | 
| Moosa 
 | 11000 | 
| Moosa 
 | 14000 | 
| Feroz | 12000 | 
| Feroz | 15000 | 
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