If the grouping column contains a null value, that row becomes a group in the results. If the grouping column contains more than one null value, the null values are put into a single group.
The royalty column in the titles table contains some null values. Here's an example that uses GROUP BY and the royalty column:
SELECT royalty, AVG(price * 2) |
||
FROM titles |
||
GROUP BY royalty |
||
royalty |
||
------- |
------ |
|
(null) |
(null) |
|
10 |
53.88 |
|
12 |
63.79 |
|
14 |
23.90 |
|
16 |
45.90 |
|
24 |
14.95 |
|
(6 row(s) affected) |
||