Question

Sort of the reverse of finding duplicate rows. I have a table with a bunch of columns, and I want to find where data isn’t the same in two columns. So…

If I have this:

------------
col1 | col2
------------
  A  |  1
------------
  A  |  1
------------
  A  |  2
------------
  B  |  1
------------
  B  |  1
------------
  B  |  3
------------
  B  |  1
------------

I want to find this:

------------
col1 | col2
------------
  A  |  1
------------
  A  |  2
------------
  B  |  1
------------
  B  |  3
------------

But if I have this:

------------
col1 | col2
------------
  A  |  1
------------
  A  |  1
------------
  B  |  1
------------
  B  |  1
------------
  B  |  1
------------

I want to find this:

Empty set

Answer 1

If we can assume you have a unique id column also, you can do something like

select *
from the_table t
where not exists (
    select 0
    from the_table t2
    where t.col1 = t2.col1
    and t.col2 = t2.col2
    and t.id < t2.id
)