Work around the 61 table JOIN limit in MySQL by nesting subqueries within each other

Question

I figured out that you can get around the 61 table join limit in MySQL by using subqueries. https://stackoverflow.com/a/20134402/2843690

I\'m trying to figure out ho

Answer 1

You're right that joining too many attributes through an EAV design is likely to exceed the limit of joins. Even before that, there's probably a practical limit of joins because the cost of so many joins gets higher and higher geometrically. How bad this is depends on your server's capacity, but it's likely to be quite a bit lower than 61.

So querying an EAV data model to produce a result as if it were stored in a conventional relational model (one column per attribute) is problematic.

Solution: don't do it with a join per attribute, which means you can't expect to produce the result in a conventional row-per-entity format purely with SQL.

I'm not intimately familiar with the Magento schema, but I can infer from your query that something like this might work:

SELECT cpe.entity_id
, o.value AS option
, v.value AS option_value
FROM catalog_product_entity AS cpe
INNER JOIN catalog_product_entity_int AS i 
  ON cpe.entity_id = i.entity_id AND i.attribute_id IN (2,3,4)
INNER JOIN eav_attribute_option AS o 
  ON i.value = o.option_id AND i.attribute_id = o.attribute_id
INNER JOIN eav_attribute_option_value AS v
  ON v.option_id = o.option_id;

The IN(2,3,4,...) predicate is where you specify multiple attributes. There's no need to add more joins to get more attributes. They're simply returned as rows rather than columns.

This means you have to write application code to fetch all the rows of this result set and map them into fields of a single object.

From comments by @Axel, is sounds like Magento provides helper functions to do this consuming of a result set and mapping it into an object.