Question

How would I go about counting values that appear in column 1, but not column 2. They are from the same table, without using subqueries or anything fancy. They may or may not share other common column values (like col 3 = col 4) but this doesnt matter.

I have it almost working with subqueries, but cannot figure how to do it without. The only problem (I think) is it will count something twice if the primary key (composed of col1,col3,col4) are different but col1 is the same.

SELECT DISTINCT COUNT(*)
FROM mytable t1
WHERE NOT EXISTS (
  SELECT DISTINCT *
  FROM mytable
  WHERE t1.column1 = mytable.column2
);

But like I said, I’m trying to figure this without subqueries anyways

Answer 1

How about:

SELECT COUNT(*)
FROM mytable mt1
  LEFT JOIN mytable mt2 ON mt1.column1 = mt2.column2
WHERE mt2.column IS NULL