Question

I need to generate XML file from all products in database (around 600 000). Problem is that i need to put into that file for every product his categories and his codes. Some products have 30 categories and 10 codes and that really hurts. Is it possible somehow to make this in single effective query or can you give me a tip how to improve my current solution:

SELECT * FROM products

and then for every product Im fetching codes and categories:

SELECT * FROM categories WHERE productid=[productid]

and

SELECT * FROM codes WHERE productid=[productid]

Thanks for any advices

Answer 1

Maybe you could play with GROUP_CONCAT:
http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

SELECT
  products.*,
  all_prod_categories.*
  all_prod_codes.*

FROM products

INNER JOIN
  (SELECT
     -- Who guarantees that all fields will be concated in the same order?
     -- Nobody :)
     GROUP_CONCAT( categories.id            ) AS all_prod_cat_ids,
     GROUP_CONCAT( categories.category_name ) AS all_prod_cat_names,
     ...
   FROM     categories
   GROUP BY categories.productid
  ) AS all_prod_categories ON categories.productid = products.id

INNER JOIN
  (SELECT
     GROUP_CONCAT( codes.id        ) AS all_prod_code_ids,
     GROUP_CONCAT( codes.code_name ) AS all_prod_code_names,
     ...
   FROM     codes
   GROUP BY codes.productid
  ) AS all_prod_codes ON codes.productid = products.id