Some useful SQL queries for Oracle database

Oracle-queries

-- SQL Query to find  employees with top three salaries
select * from (
select * from employees order by salary desc)
wHERE rownum <= 3

--SQL query for top three distinct salaries

select * from (
select distinct(salary) from employees order by salary desc)
wHERE rownum <= 3


-- SQL query to find the employee with max salary
SELECT e.SALARY, E.FIRST_NAME 
FROM employees e 
where e.salary = (SELECT MAX(Salary) FROM employees)

-- Alternative solution to find the employee with max salary 
select * 
from(select * from employees order by salary desc)
where rownum <2


-- Second highest salary
SELECT MAX(Salary) FROM employees
WHERE Salary NOT IN (SELECT MAX(Salary) FROM employees )

-- SQL query - Select Nth row
select *
  from
  (
    select
        salary
          ,dense_rank() over (order by salary desc) ranking
    from   employees
  )
  where ranking = 4 -- Replace 4 with any value of N



--Displays odd only employees
select * from
    (select first_name, last_name, salary, rownum rn
   from employees
   order by employee_id)
    where  mod (rn, 2) <> 0;

--Displays even employees
select * from
    (select first_name, last_name, salary, rownum rn
   from employees
   order by employee_id)
    where  mod (rn, 2) = 0;