nidvt0Ut

1SKU
2aaaa
3bbbb
4bbbb
5NULL
6	
7select *
8from TEST as N                                      
9where  N.SKU NOT IN (select SKU
10                     from TEST
11                     group by SKU
12                     having count(*)>1);
13	
14select SKU
15from TEST
16group by SKU
17having count(*)>1
18	
19drop table if exists TEST;
20create table TEST(
21SKU varchar(255)
22);
23insert into TEST values('aaaa'),('bbbb'),('bbbb'),(NULL);