SQL在多列中找到至少一个不为空

Question

I have a table with few non key attributes. I would like to know how can I write a query to find the key columns where I can find not nulls in any one row of these.

For example 1:

Key1 Key2 NonKey1 NonKey2    
k1   k2   nk1      nk2    
k1   k2   null     nk2    
k1   k2   nk1      null  

For example 2:

Key1 Key2 NonKey1 NonKey2 NonKey3    
k1   k2   null     nk2     nk3
k1   k2   nk1      nk2     null

Expected:

Key1 Key2 NonKey1 NonKey2
k1   k2   nk1      nk2

Answer 1

Do you simply want to grab one value per non-key column?

select key1, key2, max(nonkey1), max(nonkey2)
from mytable
group by key1, key2;

Answer 2

Something like this:

    select key1, key2, max(nonkey2), max(nonkey3)
    from MyTable
    having max(nonkey2) is not null or max(nonkey3) is not null
    group by key1, key2

(This is SQL Server, but you get the idea.)

Answer 3

other method:

select distinct key1, key2
from MyTable
where nonkey2 is not null and nonkey3 is not null