How to optimize a UNION mysql query with multiple select queries? - php

Question

I've a requirement to show the similar products in product detail page in such a way that the products listed should match the current product properties in a hierarchical way as given below
Size, color, category, company should match with the current product
Size, color, category should match with the current product
Size, color should match with the current product
Size should match with the current product
My sql query is as given below:
(SELECT pd.product_id, pd.name, p.price
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.category_id = '3' AND
pd.company_id = '1' AND
pd.product_id != '53' AND
p.status = '1'
ORDER BY RAND() LIMIT 10
)
UNION
(SELECT pd.product_id, pd.name, p.price
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.category_id = '3' AND
pd.product_id != '53' AND
p.status = '1'
ORDER BY RAND() LIMIT 10
)
UNION
(SELECT pd.product_id, pd.name, p.price
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.product_id != '53' AND
p.status = '1'
ORDER BY RAND() LIMIT 10
)
UNION
(SELECT pd.product_id, pd.name, p.price
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.product_id != '53' AND
p.status = '1'
ORDER BY RAND() LIMIT 10
)
53 - current product id and status denotes available!
Is there any way to optimize the above query?
Note Output required: We need 10 similar products. If there exists 4 products matching condition 1, then they need to listed at first in random order. Similarly we need to list the products matching other conditions below it.
Thanks in Advance!

Answer 1

Keeping using ORDER BY RAND() (which is not efficient) then a very basic improvement would be to add a priority for each clause, move the order clause to the end so it is only needed once.
(SELECT pd.product_id, pd.name, p.price , 1 AS recpriority
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.category_id = '3' AND
pd.company_id = '1' AND
pd.product_id != '53' AND
p.status = '1'
)
UNION
(SELECT pd.product_id, pd.name, p.price , 2 AS recpriority
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.category_id = '3' AND
pd.product_id != '53' AND
p.status = '1'
)
UNION
(SELECT pd.product_id, pd.name, p.price , 3 AS recpriority
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.color_id = '2' AND
pd.product_id != '53' AND
p.status = '1'
)
UNION
(SELECT pd.product_id, pd.name, p.price , 4 AS recpriority
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE
pd.size_id = '33' AND
pd.product_id != '53' AND
p.status = '1'
)
ORDER BY recpriority, RAND() LIMIT 10
That could then be done without the need for unions by doing something like this:-
SELECT pd.product_id,
pd.name,
p.price ,
CASE
WHEN pd.color_id = '2' AND pd.category_id = '3' AND pd.company_id = '1' THEN 1
WHEN pd.color_id = '2' AND pd.category_id = '3' THEN 2
WHEN pd.color_id = '2' THEN 3
ELSE 4
END AS recpriority
FROM mg_product_description pd
JOIN `mg_product` p ON p.product_id = pd.product_id
WHERE pd.size_id = '33'
AND pd.product_id != '53'
AND p.status = '1'
ORDER BY recpriority, RAND()
LIMIT 10