Write an SQL query to count the number of employees in each department.

You can use GROUP BY to aggregate employees per department and COUNT to get the number of rows in each group. The query is:

SELECT department, COUNT(*) AS employee_count

FROM Employee

GROUP BY department

ORDER BY department;

This query groups all rows by the department column, counts how many rows belong to each group, and returns the department name along with the count. The ORDER BY clause is optional but makes the output easier to read. The time complexity is O(n) because each row is processed once during grouping.