用于查找每个组中成员相同的记录的 SQL 查询

Question

I am sorry for the basic question. I have a table with two columns and I would like to extract Gene with Class = M (my expected output below). I tried where Class = 'P' and Group by Gene, but still I have both Gene a and b as outputs. Can you help me please?

Gene    Class
a   m
a   m
a   m
b   p   
b   m
b   p
c   p
c   p   
c   p

This is what I expect to have..

Gene    Class
a   m

Thank you very much in advance!

Answer 1

You can use aggregation and having if class always has to have the same value:

select gene, min(class)
from t
group by gene
having min(class) = max(class) and min(class) = 'm';

Here is a db<>fiddle.