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

Regards, 

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