How to find rows where column A is seen with multiple values of column B (and vice versa)

Question

Given the following schema, I'd like to return rows where A or B appear in more than one row that is not a single pairing.

For example:

fruitl + fruitU should be the only combination seen in the table. Eg apple + Apple is okay, but if we see apple + APple or Apple + Apple then there is an issue with data quality.

Essentially A + B should be a unique combo.

 fruitl | fruitu | ...
----------------------
 apple  | Apple  | ...
 apple  | Apple  | ...
 apple  | APple  | ...
 banana | Banana | ...
 banana | Banana | ...
 peach  | Peach  | ...
 peach  | Peach  | ...

From the above table the query would show...

apple | APple

or

apple | Apple

since apple is paired with two unique values.

I have been approaching it using something like the below but that only seems to return distinct values.

There are an unlimited number of potential fruits in the database.

select *
from table
group by fruitl, fruitu
having count(*) > 1;

Answer 1

Hmmm, I think you want something like this:

select t.*
from table t
where (A in ('a', 'b') or B in ('a', 'b')) and not (A = 'a' and B = 'b');

I'm not sure if you also want not (A = 'b' and B = 'a') . The question is unclear about this combination.

There are other ways to express the logic, but this seems to most closely match your description.