SQL Server Aggregate Functions: COUNT Explained

Count Employees by Department

Write a query to count the number of employees in each department using COUNT and GROUP BY.

Expected output: A list of departments with the count of employees in each.

Hint: Use COUNT(*) and GROUP BY Department.

Count Non-Null Phone Numbers

Write a query to count how many employees have a phone number recorded (non-null).

Expected output: A single number representing employees with phone numbers.

Hint: Use COUNT on the PhoneNumber column.

COUNT(*) counts all rows including those with NULLs, while COUNT(column_name) counts only non-null values in that column.

No, COUNT(DISTINCT column_name) counts unique non-null values only; NULLs are excluded.

COUNT helps summarize data by providing the number of rows or values that meet specific criteria, essential for reporting and insights.