Our queries are getting fairly complex, but we have nearly introduced all the important parts of a
SELECT query. One thing that you might have noticed is that if the
GROUP BY clause is executed
WHERE clause (which filters the rows which are to be grouped), then how exactly do we
filter the grouped rows?
Luckily, SQL allows us to do this by adding an additional
HAVING clause which is used specifically
GROUP BY clause to allow us to filter grouped rows from the result set.
SELECT group_by_column, AGG_FUNC(column_expression) AS aggregate_result_alias, … FROM mytable WHERE condition GROUP BY column HAVING group_condition;
HAVING clause constraints are written the same way as the
WHERE clause constraints, and are
applied to the grouped rows. With our examples, this might not seem like a particularly useful
construct, but if you imagine data with millions of rows with different properties, being able to apply
additional constraints is often necessary to quickly make sense of the data.
If you aren't using the `GROUP BY` clause, a simple `WHERE` clause will suffice.
For this exercise, you are going to dive deeper into Employee data at the film studio. Think about the different clauses you want to apply for each task.