Data Analytics & SQL Mastery: 20 Real-World Interview Queries with Window Functions & CTEs

1. The 5 SQL Concepts Tested in 95% of Technical Screens

Data team interviewers evaluate whether you can write clean, performant SQL without redundant subqueries or memory-heavy self-joins.

2. High-Frequency SQL Patterns & Solutions

Q1: Find the 2nd Highest Salary per Department (Handling Ties).

Solution using DENSE_RANK():

WITH RankedSalaries AS (
  SELECT 
    department_id,
    employee_id,
    salary,
    DENSE_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) as rank_num
  FROM employees
)
SELECT department_id, employee_id, salary
FROM RankedSalaries
WHERE rank_num = 2;

Q2: Calculate a 7-Day Rolling Revenue Average.

SELECT 
  order_date,
  daily_revenue,
  AVG(daily_revenue) OVER (
    ORDER BY order_date
    ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
  ) as rolling_7d_avg
FROM daily_sales_summary;

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