Capgemini SQL Interview Question | Days Since First Purchase (GROUP BY vs Window Functions)

🚀 In this video, we solve a popular SQL interview question step by step! Learn how to: ✔️ Find the first purchase date per user ✔️ Calculate days since first purchase ✔️ Use GROUP BY and MIN() effectively ✔️ Understand Window Functions (PARTITION BY) 💡 This is a must-know concept for Data Analyst, Data Scientist, and SQL interviews. 📊 Problem Statement You are given a purchases table with: USER_ID PURCHASE_DATE 👉 Task: Find the first purchase date for each user Calculate days since that purchase 🧠 Concepts Covered Aggregations (MIN) GROUP BY Window Functions PARTITION BY Date Arithmetic in SQL --Create Table CREATE TABLE purchases ( USER_ID INT, PURCHASE_DATE DATE ); --Insert Data INSERT INTO purchases (USER_ID, PURCHASE_DATE) VALUES (1, '2023-01-10'), (1, '2023-02-15'), (1, '2023-03-20'), (2, '2023-05-05'), (2, '2023-06-01'), (3, '2024-01-12'), (3, '2024-02-18'), (3, '2024-03-25'), (4, '2025-07-01'); SQL Interview QnAs: https://www.youtube.com/playlist?list=PLL871c9yfLoimvglCSz6UQoqLJcFBJGKo ***Join our Telegram Group for regular updates on Jobs and Data Science materials: https://t.me/skilltechathon Follow us on Instagram: https://www.instagram.com/skilltechathon/ #sql #postgresql #deloitte #deloittejobs #capgeminihiring #mysql #interview #dataengineering #dataanalytics #dataanalysis #capgemini #capgeminijobs #sqlfordataengineer #jobinterview #coding #programming #technicalinterview