Problem with INNER JOIN query - very long executing - mysql

Question

I observed a problem when I use INNER JOIN query. When I use query without INNER JOIN, all work very fast. When I add INNER JOIN, the query executes very long. It's my query:
SELECT
component_offer_unconnected.id AS id,
component_offer_unconnected.title AS NAME,
component_offer_unconnected.ean AS ean,
component_offer_unconnected.productCode AS productCode,
component_offer_unconnected.tmpImg AS tmpImg,
component_offer_unconnected.userAccountName AS userAccountName,
component_offer_unconnected.userAccountId AS userAccountId,
component_offer_unconnected.complete AS complete,
component_offer_unconnected.active AS active,
component_offer_unconnected.stockAvailable AS stockAvailable
FROM
component_offer_unconnected
INNER JOIN products ON(
(
products.productCode = component_offer_unconnected.productCode AND component_offer_unconnected.productCode != ''
) AND(
products.ean = component_offer_unconnected.ean AND component_offer_unconnected.ean != ''
)
)
ORDER BY
component_offer_unconnected.id
DESC

Answer 1

The query can benefit from the following indexes:
create index ix1 on component_offer_unconnected (id, productCode, ean);
create index ix2 on products (productCode, ean);
If you can add them, the query could experience a performance improvement. If it doesn't please post the new execution plan.
Now, your query as it is, can potantially find multiple matches for each row. If you want each row to show up only once you can use EXISTS instead, as in:
SELECT
id AS id,
title AS NAME,
ean AS ean,
productCode AS productCode,
tmpImg AS tmpImg,
userAccountName AS userAccountName,
userAccountId AS userAccountId,
complete AS complete,
active AS active,
stockAvailable AS stockAvailable
FROM component_offer_unconnected u
WHERE u.productCode != ''
AND u.ean != ''
AND EXISTS (
SELECT 1
FROM products p
WHERE p.productCode = u.productCode
AND p.ean = u.ean
)
ORDER BY id DESC