Let’s revisit the query we wrote to count the number of students.
Let’s say if instead of counting all students, we want to count the number of students in each grade.
This involves grouping students as per their grades, and then apply count on each group.
SQL provides clause
GROUP BY to achieve that.
Observe that in the result of above query, there is a row where the
grade value is
NULL. That’s expected, because even in
GROUP BY clause, a
grade is still a unique grade.
There are students with a
grade, so they appear in the results of the query.
If we want to skip the results with
NULL grade, we can filter them out by adding a simple