K	P	G
1	0	red
2	NULL	red
3	0	blue
4	9	red
5	NULL	blue

Table T has 5 rows of 3 columns of data as shown above, where NULL means no data.

The following statement

SELECT P, COUNT(*) as Total

FROM T

GROUP BY P

HAVING COUNT(*) = 1;

should return a table containing

a.) zero row b.) 1 row c.) 2 rows d.) 3rows