🔎 SQL HAVING – Filter Grouped Results After Aggregation

🧲 Introduction – What is SQL HAVING?

The HAVING clause in SQL is used to filter aggregated results after a GROUP BY operation. Unlike WHERE, which filters individual rows before grouping, HAVING applies conditions to grouped rows.

🎯 In this guide, you’ll learn:

• Syntax and difference between WHERE and HAVING
• How to filter results using aggregate functions
• Best practices for using HAVING with GROUP BY

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✅ 1. HAVING Syntax

SELECT column, AGG_FUNCTION(column)
FROM table
GROUP BY column
HAVING AGG_FUNCTION(column) condition;

✅ Used to filter grouped results based on aggregation.

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📊 2. Example – Filter Groups by Total

SELECT customer_id, SUM(amount) AS total_spent
FROM orders
GROUP BY customer_id
HAVING SUM(amount) > 1000;

✅ Shows customers who spent more than $1,000.

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🔍 3. WHERE vs HAVING

Clause	Filters Before Grouping	Filters After Grouping	Supports Aggregates
WHERE	✅	❌	❌
HAVING	❌	✅	✅

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🔄 4. Using WHERE with HAVING Together

SELECT department, AVG(salary) AS avg_salary
FROM employees
WHERE salary > 0
GROUP BY department
HAVING AVG(salary) > 50000;

✅ Filters low salaries early with WHERE, then filters high-average groups with HAVING.

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🧠 5. HAVING with COUNT(), MAX(), MIN()

SELECT status, COUNT(*) AS total
FROM orders
GROUP BY status
HAVING COUNT(*) > 10;

✅ Keeps only order statuses that appear more than 10 times.

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📘 Best Practices

✅ Recommended	❌ Avoid This
Use HAVING for aggregate conditions	Using WHERE with aggregate functions
Combine WHERE and HAVING efficiently	Filtering grouped data too late
Use aliases for readability	Repeating full expressions

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📌 Summary – Recap & Next Steps

The HAVING clause lets you refine grouped results, filtering by aggregated values. It’s essential for analytics and summary queries.

🔍 Key Takeaways:

• Use HAVING after GROUP BY
• Required when filtering with COUNT(), SUM(), AVG(), etc.
• Combine with WHERE for row-level filtering

⚙️ Real-World Relevance:
Used in reports, dashboards, business summaries, and performance KPIs.

➡️ Next: Explore advanced grouping tools like ROLLUP, CUBE, and WINDOW FUNCTIONS.

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❓ FAQ – SQL HAVING

❓ What is the difference between HAVING and WHERE?

✅ WHERE filters rows before grouping. HAVING filters after aggregation.

❓ Can I use HAVING without GROUP BY?

✅ Yes—but only if used with an aggregate function.

❓ Do aliases work in HAVING?

❌ Not in all databases. It’s safer to repeat the full aggregate.

❓ Can I use HAVING with multiple conditions?

✅ Yes, combine them with AND/OR just like WHERE.

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