1. COUNT():

   • COUNT() is used to count the number of rows in a result set or the number of non-null values in a column.

   Example 1:

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   SELECT COUNT(*) AS total_orders
   FROM orders;
   
   

   Output: The total number of orders in the "orders" table.

   Example 2:

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   SELECT customer_id, COUNT(order_id) AS order_count
   FROM orders
   GROUP BY customer_id;
   
   

   Output: The count of orders for each customer.

2. SUM():

   • SUM() calculates the sum of values in a numeric column.

   Example:

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   SELECT SUM(total_amount) AS total_sales
   FROM sales;
   
   

   Output: The total sales amount.

3. AVG():

   • AVG() calculates the average value of numeric data in a column.

   Example:

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   SELECT AVG(score) AS average_score
   FROM exam_results;
   
   

   Output: The average exam score.

4. MIN() and MAX():

   • MIN() and MAX() return the minimum and maximum values in a column, respectively.

   Example 1:

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   SELECT MIN(price) AS lowest_price
   FROM products;
   
   

   Output: The lowest product price.

   Example 2:

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   SELECT MAX(salary) AS highest_salary
   FROM employees;
   
   

   Output: The highest employee salary.

5. GROUP_CONCAT() (MySQL-specific):

   • GROUP_CONCAT() concatenates values from multiple rows into a single string within each group.

   Example:

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   SELECT department, GROUP_CONCAT(employee_name) AS employees_list
   FROM employees
   GROUP BY department;
   
   

   Output: A comma-separated list of employees' names in each department.

6. STDEV() and VAR():

   • STDEV() calculates the standard deviation, and VAR() calculates the variance of a set of values.

   Example:

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   SELECT department, STDEV(salary) AS salary_std_dev, VAR(salary) AS salary_variance
   FROM employees
   GROUP BY department;
   
   

   Output: The standard deviation and variance of salaries in each department.

7. BIT_AND() and BIT_OR():

   • BIT_AND() performs a bitwise AND operation, and BIT_OR() performs a bitwise OR operation on a set of values.

   Example:

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   SELECT department, BIT_AND(permission) AS all_permissions, BIT_OR(permission) AS any_permission
   FROM user_permissions
   GROUP BY department;
   
   

   Output: The combined bitwise AND and OR results for permissions in each department.

8. COUNT(DISTINCT column):

   • COUNT(DISTINCT column) counts the number of distinct (unique) values in a column.

   Example:

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   SELECT COUNT(DISTINCT product_category) AS unique_categories
   FROM products;
   
   

   Output: The count of unique product categories.

These aggregate functions are used to summarize and analyze data in SQL queries. They allow you to perform calculations on groups of rows, calculate statistics, and generate aggregated results based on specific criteria.