Learn SQL
JOINS - Grouping


Let’s say we want to display the names of all unique courses and the total number of students enrolled in each course.

In this case, we can use COUNT over GROUP BY clause for the number of students, over the JOIN of tables students and courses.

Take a close look at the results, not all courses are included in the records. Course C, that does not have any students enrolled in it, doesn’t show up. We need to use a LEFT OUTER JOIN/LEFT JOIN in this case, keeping courses at the left, so that all the records from courses show up, irrespective of matching records from the table at the right.