Day 25/30 - DEEP DIVE SOLUTIONS: SQL, PYTHON, ETL, DATA MODELING
Solutions for March 28th, 2025 Challenge – Full Breakdown + Live Runnable Code
Hello Data Engineers,
You’re wrapping up Week 5 with foundational concepts that come up constantly: group filtering with HAVING, Python string methods, data validation before loading, and the difference between OLTP and OLAP systems. Let's break each one down into usable, testable knowledge.
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SQL Deep Dive: Group Filtering with HAVING
Challenge Recap:
❓ Which clause is used to filter after an aggregation has been applied?
🔘 A) WHERE
🔘 B) FILTER
🔘 C) HAVING
🔘 D) JOIN
✅ Answer: Option C - HAVING
Why This Happens:
WHERE filters individual rows before aggregation, while HAVING filters after grouping has occurred. It’s used to return only the groups that match your condition.
Where It’s Used in Real-World Applications:
Returning only products with high sales volume
Filtering customer groups with high average spend
Identifying underperforming teams or regions