Consider the employee table with the fields emp_id and salary.
Now if you want get the 1st highest salary then you can use the below query
SELECT DISTINCT `salary` FROM `employee`ORDER BY `salary` DESC LIMIT 0, 1
To find the 2nd highest salary then you can use the following query
SELECT DISTINCT `salary` FROM `employee`ORDER BY `salary` DESC LIMIT 1, 1
Likewise you can find the any of the highest salary using the above query by changing the LIMIT value
Also you can find the highest salary in many other ways but this one of the easy way to find the highest salary.
Note: This is the most common question asked in many of the interviews