SQL & PL/SQL :: Getting Most Common Value

I am using this query:

Select
t1.col1 as A,
t2.col1 as B,
t3.col1 as C,
t4.col1 as D

[Code]...

with this above query i am getting result like this:

A B C D

2 null 2 null
6 6 null 6
8 null null null

However i need the result like this:

A B C D

6 6 null 6

Note:

I am looking for common value that presents in most of these 4 tables for different t1.col2 values like 'E','G','K',...etc. I cant use the NOT NULL condition in the where clause,since i need to check for different values in t1.col2,for each of this there may be null value in any of the 4 tables.