SQL for Beginners #5 (HackerRank) – Count Total and Unique Cities in Station

Описание: In this first SQL tutorial from The Daily Commit, we solve one of the most common beginner problems from HackerRank:
difference between COUNT(*) and COUNT(DISTINCT ...)
You’ll learn:
✅ The difference between COUNT(*) and COUNT(DISTINCT column)
✅ How to use aggregate functions in SQL
✅ How to perform simple calculations inside a SELECT statement

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🎓 Playlist: HackerRank SQL for Beginners to Advanced | The Daily Commit