Question

I have a table such as:

table a
+------+-------+
| v1   | v2    |
+------+-------+
|    1 | one   |
|    2 | two   |
|    3 | two   |
|    4 | two   |
|    5 | NULL  |
|    6 | NULL  |
|    7 | three |
|    8 | three |
+------+-------+

I want to group the data in this table by the column ‘v2’…

mysql> select * from a group by v2 order by v1;
+----+-------+
| v1 | v2    |
+----+-------+
|  1 | one   |
|  2 | two   |
|  5 | NULL  |
|  7 | three |
+----+-------+

… but leave the NULL values on separate rows. Is it possible to prevent the NULL values from being collapsed into a single row?

Answer 1

This would accomplish what you’re asking:

select min(v1) as v1, v2 from a group by v2, ifnull(v2, v1) order by v1;

This would group by v2, unless it is NULL, in which case it would group by v1. Since your two NULL values have two different values for v1, it would split them apart.