06. Video: SUM
SUM
Unlike COUNT, you can only use SUM on numeric columns. However, SUM will ignore NULL values, as do the other aggregation functions you will see in the upcoming lessons.
Aggregation Reminder
An important thing to remember: aggregators only aggregate vertically - the values of a column. If you want to perform a calculation across rows, you would do this with simple arithmetic.
We saw this in the first lesson if you need a refresher, but the quiz in the next concept should assure you still remember how to aggregate across rows.