It's time to wrap things up for this part. First, let's review what we learned:
- SQL reports often require joining a lot of tables.
- Every column listed in the
SELECT statement that's NOT used with an aggregate function must appear in the
GROUP BY clause.
- Not every column from the
GROUP BY clause must appear in the
- Watch out when using
|Type of count
||What is counted
||rows with non-NULL values in
||only the unique non-NULL values in
- Avoid using
LEFT JOINs with
How about a short quiz before we start the next part?