If a table have column A and B
Count(distinct A) as Da
Count(distinct B) as Db
Count(distinct A, B) as Dab
The Da/Db<=Dab, this will be always true;
1. if(Da=Db=Dab) => A:B as 1:1
2. if(Da<(Db=Dab)) => A:B as 1:N
3. if(Db<(Da=Dab)) => A:B as N:1
4. if(Da!=Db!=Dab) => A:B as N:N //relashionship is mess
For example for 4, how to generate the smaple data, first build a 1:N and then change the column to be N:N, like below
1 2
1 3
1 4
2 5
=>
1 2
1 3
1 4
2 4
Da=2, Db=3,Dab=4