Itzik Ben-Gan takes us through four bugs or oddities around joins:
The order counts are now correct, but the total freight values are not. Can you spot the new bug?
The new bug is more elusive because it manifests itself only when the same customer has at least one case where multiple orders happen to have the exact same freight values. In such a case, you are now taking the freight into account only once per customer, and not once per order as you should.
Click through to avoid accidentally introducing bugs in your T-SQL code.