What is the difference between the GROUP BY and ORDER BY clauses in SQL and how do they work with data?

The GROUP BY instruction is used to group rows with the same values in specified columns. It is often used together with aggregate functions (such as COUNT, SUM, AVG) to obtain summary data for groups.

Example:

SELECT department, COUNT(*) AS employee_count
FROM employees
GROUP BY department;

This query counts the number of employees in each department.

The ORDER BY instruction is used to sort the query result by one or more columns, in ascending (ASC) or descending (DESC) order.

Example:

SELECT * FROM employees
ORDER BY salary DESC;

This query will display all employees sorted by salary from highest to lowest.

Thus, GROUP BY aggregates data by groups, and ORDER BY sorts the final data set.