Java 8 Stream API: 8 Interview Questions You Should Be Able to Answer
Streams appear in almost every Java interview. Here are common Stream API questions with clear explanations and code you can practise.
Sample article
Joins, GROUP BY, the classic “second highest salary” and window functions — practise these SQL questions before your next interview.
Whether you are a Java Full Stack or MEAN Stack developer, SQL rounds are common. These questions appear again and again — practise writing them by hand.
1. Second highest salary
SELECT MAX(salary) AS second_highest
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);2. Nth highest salary with a window function
SELECT salary
FROM (
SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS rnk
FROM employees
) ranked
WHERE rnk = 3;3. Departments with more than five employees
SELECT department_id, COUNT(*) AS employee_count
FROM employees
GROUP BY department_id
HAVING COUNT(*) > 5;WHERE filters rows before grouping; HAVING filters groups after aggregation.
4. Find duplicate emails
SELECT email, COUNT(*)
FROM users
GROUP BY email
HAVING COUNT(*) > 1;INNER JOIN returns only matching rows from both tables. LEFT JOIN returns all rows from the left table, with NULLs where the right table has no match.
This is a sample article published as a starter resource. Verify technical details against official documentation for the versions you use.