Unpivot Quarterly Columns

The table stores one column per quarter. Turn it into rows with the columns product, quarter and amount, ordered by product then quarter.

Table schema

Sales(product VARCHAR(20), q1 INT, q2 INT, q3 INT, q4 INT)

Sample data

product | q1 | q2 | q3 | q4
Pen | 10 | 20 | 30 | 40
Book | 1 | 2 | 3 | 4