What are aggregate functions?

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Aggregate functions in SQL are special functions that perform a calculation on a set of values and return a single summarized value. They are commonly used with the GROUP BY clause to group rows and compute statistics on them, though they can also be used without grouping to summarize entire tables.

🔹 Common Aggregate Functions:

1. COUNT() – Returns the number of rows (e.g., COUNT(*) counts all rows, COUNT(column) counts non-null values).

2. SUM() – Adds up all values in a numeric column.

3. AVG() – Calculates the average value of a numeric column.

4. MIN() – Finds the smallest value.

5. MAX() – Finds the largest value.

🔹 Example:

SELECT department, AVG(salary) AS avg_salary,
       SUM(salary) AS total_salary,
       COUNT(*) AS employee_count
FROM employees
GROUP BY department;

This query gives the average salary, total salary, and number of employees for each department.

🔹 Key Points:

• Aggregate functions ignore NULL values (except COUNT(*)).

• They are often used in reporting, analytics, and dashboards.

• Can be combined with HAVING to filter groups based on aggregated results.

✅ Summary: Aggregate functions are essential for summarizing large datasets into meaningful insights, such as totals, averages, counts, minimums, and maximums.

Read More :

How do you find duplicates in a table?

What is a window function in SQL?

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