MySQL self-join for an EAV based stock control application

Question

This question relates to the schema I suggested in my original question regarding a stock control application.

I'm trying to create a MySQL query that provides the current stock for a particular item.

The query is working but I wondered whether there is a more efficient way of obtaining the information I require.

SELECT 's'.*,
    'v1'.'attribute_id' AS 'att1',
    'v1'.'value' AS 'val1'
    'v2'.'attribute_id' AS 'att2',
    'v2'.'value' AS 'val2'
FROM 'eav_ev' AS 'ev1'
INNER JOIN 'stock' AS 's' ON s.id = ev1.stock_id
INNER JOIN 'eav_ev' AS 'ev2' ON ev1.stock_id = ev2.stock_id
INNER JOIN 'eav_value' AS 'v1' ON v1.id = ev1.value_id
INNER JOIN 'eav_value' AS 'v2' ON v2.id = ev2.value_id
WHERE (ev1.entity_id = '45')
    AND (ev1.value_id <> ev2.value_id)
    AND (s.total > 0)
GROUP BY 'ev1'.'stock_id'
ORDER BY 'ev1'.'value_id' ASC

This returns something along the lines of

array (1) {
    [0] => array(5) {
        ["stock_id"] => "2"
        ["att1"] => "3"
        ["val1"] => "M12"
        ["att2"] => "4"
        ["val2"] => "45"
    }
}

It seems very messy but my poor brain is incapable of coming up with something better.

Any suggestions?

Answer 1

Instead of using attribute_id AS att1 you could also use value AS attribute_X if you store a list of attributes first. You can simply cache the query after which you can just select all needed data in 1 clear query.

Assuming you've fetched a list of attribute IDs first (i.e. SELECT attribute_id FROM eav_value), select this:

SELECT
    v1.value_id AS attribute_1 -- (or whatever the ID was fetched in the first query)
    v2.value_id AS attribute_2 -- (or whatever the second ID was fetched in the first query)
...