Part 54: Filtering Aggregations: HAVING vs WHERE

One of the most critical distinctions in SQL is when to use WHERE versus HAVING.

1. WHERE vs HAVING

• WHERE: Filters individual rows BEFORE grouping and aggregation.
• HAVING: Filters summarized groups AFTER grouping and aggregation.

SELECT department, COUNT(*) AS head_count, AVG(salary) AS avg_sal
FROM employees
WHERE is_active = TRUE         -- 1. Filters rows first
GROUP BY department           -- 2. Groups remaining rows
HAVING COUNT(*) > 5;           -- 3. Filters groups with > 5 active employees

Key Takeaways

• Use WHERE to filter individual rows.
• Use HAVING to filter aggregated group metrics.

In Part 55, we explore Multi-Column Grouping and Aggregation Hierarchies!