- 10.1 Introduction
- 10.2 Grouping on One Column
- 10.3 Grouping on Two or More Columns
- 10.4 Grouping on Expressions
- 10.5 Grouping of NULL Values
- 10.6 General Rules for the GROUP BY Clause
- 10.7 Complex Examples with GROUP BY
- 10.8 Grouping with WITH ROLLUP
- 10.9 Grouping with WITH CUBE
- 10.10 Grouping Sets
- 10.11 Grouping with ROLLUP and CUBE
- 10.12 Combining Grouping Sets
- 10.13 Answers
10.5 Grouping of NULL Values
If grouping is required on a column that contains NULL values, all these NULL values form one group. When rows are grouped, NULL values are also considered to be equal. The reason is that, with a GROUP BY, a vertical comparison is applied. This is in accordance with the rules described in Section 9.5, in Chapter 9, "SELECT Statement: SELECT Clause and Aggregation Functions."
Example 10.10. Find the different league numbers.
SELECT LEAGUENO FROM PLAYERS GROUP BY LEAGUENO
The result is:
LEAGUENO -------- 1124 1319 1608 2411 2513 2983 6409 6524 7060 8467 ?
Explanation: Players 7, 28, 39, and 95 do not have a league number and, therefore, form one group (the last row) in the end result.