Question

For each identifier, how can I return the quantity when the received country is not equal to any of the delivered countries? I need an efficient query for the steps below since my table is huge.

These are the steps I would think could do this, of course you don’t need to follow them 🙂

1. Create a group of ‘delivered’ countries for each identifier.
2. See if ‘received’ is any of these countries for each identifier. If
   there is no match, return this result.

Starting Table:

identifier         delivered            received        quantity
-------------      ------------         -----------     ------------
1                  USA                  France          432
1                  France               USA             450
1                  Ireland              Russia          100
2                  Germany              Germany         1,034
3                  USA                  France          50
3                  USA                  USA             120

Result:

identifier         delivered            received        quantity
-------------      ------------         -----------     ------------
1                  Ireland              Russia          100 

The starting table is about 30,000,000 rows, so self-joins will be impossible unfortunately. I am using something similar to MySQL.

Answer 1

I think LEFT JOIN query should work for you:

SELECT a.*
FROM starting a
     LEFT JOIN starting b
        ON a.id = b.id
           AND a.delivered = b.received
WHERE b.received IS NULL;

Example: SQLFiddle

For optimizing above query, adding following composite index should give you better performance:

ALTER TABLE starting  ADD KEY ix1(id, delivered, received);