Question

supposed I have a table with three columns: user_to, user_from, counter. I’m trying to do a query that checks does a cross reference check from the same table. Maybe this will help understand:

SELECT user_to AS user_to1
    , user_from AS user_to2
FROM tbl
WHERE counter > 10
    AND NOT EXISTS (
        SELECT *
        FROM tbl
        WHERE user_to = user_from1
            AND user_from = user_to1
        )

I assume I’m trying to do it wrong, but the query helps to understand what I’m trying to accomplish.

Answer 1

you can add an ALIAS on it,

SELECT user_to AS user_to1
    , user_from AS user_to2
FROM tbl a
WHERE counter > 10
    AND NOT EXISTS (
        SELECT *
        FROM tbl b
        WHERE b.user_to = a.user_to
            AND b.user_from = a.user_from
        )