✅ SQL GROUP BY HAVING 📊

What is GROUP BY?
GROUP BY is used to group rows that have the same values in one or more columns. It’s mostly used with aggregate functions like SUM(), COUNT(), AVG() to get summarized results.

What is HAVING?
HAVING is like WHERE, but it works after grouping. It filters the grouped results. You can’t use aggregate functions in WHERE, so we use HAVING instead.

📌 Problem 1:
You want to find total sales made in each city.

SELECT city, SUM(sales) AS total_sales  
FROM customers  
GROUP BY city;

✅ This groups the sales by city and shows total per group.

📌 Problem 2:
Now, show only those cities where total sales are above ₹50,000.

SELECT city, SUM(sales) AS total_sales  
FROM customers  
GROUP BY city  
HAVING total_sales > 50000;

✅ `HAVING filters the result after grouping.

📌 Problem 3:
Find departments with more than 10 active employees.

SELECT department, COUNT(*) AS emp_count  
FROM employees  
WHERE active = 1  
GROUP BY department  
HAVING emp_count > 10;

✅ First, we filter rows using WHERE. Then group, then filter groups with HAVING.

💡 Use GROUP BY to summarize, HAVING to filter those summaries.

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