Question

I am new to derived queries with MySQL and am having trouble with two things.

1) How do I reference the t1.dCount so that it counts the number of xcart_images_D.productId for each optionId?

2) How can I streamline the derived SELECT of this query? (Currently this query takes 45 seconds to run)

 SELECT xp.productid, xp.product, xc.classid, xco.optionid, xco.option_name, xiW.id, xiW.image_path, t1.dCount
 FROM xcart_products xp
 INNER JOIN xcart_variants xv ON xp.productid = xv.productid
 INNER JOIN xcart_variant_items xvi ON xv.variantid = xvi.variantid
 INNER JOIN xcart_class_options xco ON xvi.optionid = xco.optionid
 INNER JOIN xcart_classes xc ON xco.classid = xc.classid AND xc.class = 'COLOR'
 LEFT JOIN xcart_images_W xiW ON xiW.id = xvi.variantid
 LEFT JOIN (
 SELECT COUNT(xiD.optionid) as dCount 
    FROM xcart_products xp2
    INNER JOIN xcart_classes xc2 ON xp2.productid = xc2.productid AND xc2.class = 'Color'
    INNER JOIN xcart_class_options xco2 ON xc2.classid = xco2.classid
    LEFT JOIN xcart_images_D xiD ON xiD.optionid = xco2.optionid
 ) as t1 ON xiW.id = xvi.variantid
 GROUP BY xco.optionid
 ORDER by xp.product DESC

Here is a working version of the count but without the derived select –

SELECT xp.productid, xp.product, xc.classid, xco.optionid, xco.option_name, xiD.image_path, xiD.path_on_server, count(xiD.optionid) as cnt
    FROM xcart_products xp
    INNER JOIN xcart_classes xc ON xp.productid = xc.productid AND xc.class = 'Color'
    INNER JOIN xcart_class_options xco ON xc.classid = xco.classid
    LEFT JOIN xcart_images_D xiD ON xiD.optionid = xco.optionid
    GROUP BY xp.product, xco.optionid
    ORDER by xp.product DESC

In case it’s needed here is the DB layout –

+ xcart_products
    - productid*
    - product
+ xcart_variants
    - variantid*
    - productid (xcart_products.productid)
+ xcart_variant_items [bridge table]
    - optionid*
    - variantid (xcart_variants.variantid)
+ xcart_classes
    - classid*
    - productid (xcart_products.productid)
    - class
+ xcart_class_options
    - optionid*
    - option_name
    - classid (xcart_classes.classid)
+ xcart_images_W
    - imageid*
    - id (xcart_variants.variantid)
    - image_path
+ xcart_images_D
    - imageid* [not relational with xcart_images_W.imageid]
    - id (xcart_products.productid)
    - optionid (xcart_class_options.optionid)

* Primary Key
() relational data
[] notes

Answer 1

Here’s your original query with some notes describing what I think is the problem:

 SELECT xp.productid, xp.product, xc.classid, xco.optionid, xco.option_name, xiW.id, xiW.image_path, t1.dCount
 FROM xcart_products xp
 INNER JOIN xcart_variants xv ON xp.productid = xv.productid
 INNER JOIN xcart_variant_items xvi ON xv.variantid = xvi.variantid
 INNER JOIN xcart_class_options xco ON xvi.optionid = xco.optionid
 INNER JOIN xcart_classes xc ON xco.classid = xc.classid AND xc.class = 'COLOR'
 LEFT JOIN xcart_images_W xiW ON xiW.id = xvi.variantid
 -- all of the above is pretty standard.

 -- but this part is a little wonky!
 LEFT JOIN (
 SELECT COUNT(xiD.optionid) as dCount 
    FROM xcart_products xp2
    INNER JOIN xcart_classes xc2 ON xp2.productid = xc2.productid AND xc2.class = 'Color'
    INNER JOIN xcart_class_options xco2 ON xc2.classid = xco2.classid
    LEFT JOIN xcart_images_D xiD ON xiD.optionid = xco2.optionid
 ) as t1 ON xiW.id = xvi.variantid
 -- The inner query here only returns one column, which means it's
 -- *not related* to anything.  That's why, outside, you're using an
 -- ON query that has nothing to do with the data inside the table 
 -- you're joining!  You need to group by in the inner select.

 GROUP BY xco.optionid
 ORDER by xp.product DESC

Try something like:

SELECT xp.productid, xp.product, xc.classid, xco.optionid, xco.option_name, xiW.id, xiW.image_path, t1.dCount
 FROM xcart_products xp
 INNER JOIN xcart_variants xv ON xp.productid = xv.productid
 INNER JOIN xcart_variant_items xvi ON xv.variantid = xvi.variantid
 INNER JOIN xcart_class_options xco ON xvi.optionid = xco.optionid
 INNER JOIN xcart_classes xc ON xco.classid = xc.classid AND xc.class = 'COLOR'
 LEFT JOIN xcart_images_W xiW ON xiW.id = xvi.variantid
 -- Keep the above

 -- but change this one to add a group by.
 LEFT JOIN (
 SELECT xco2.optionId as optionid, count(*) as dCount 
    -- this could be cleaned up if the products and class aren't
    -- really relevant- as it is, it serves only to narrow the set
    -- of xcart_class_options you'll be looking at/counting for.
    FROM xcart_products xp2
    INNER JOIN xcart_classes xc2 ON xp2.productid = xc2.productid AND xc2.class = 'Color'
    INNER JOIN xcart_class_options xco2 ON xc2.classid = xco2.classid

    -- bring in the image_ds that match the class_option we are looking
    -- at
    LEFT JOIN xcart_images_D xiD ON xiD.optionid = xco2.optionid

    -- And group by those option_ids.
    group by xid.optionid
 ) as t1 ON xco.optionid = t1.optionid
 -- we join the inner select based on the optionid we were looking at.

 GROUP BY xco.optionid
 ORDER by xp.product DESC

To make it faster, this will probably work, depending on the results you’re looking for:

SELECT xp.productid, xp.product, xc.classid, xco.optionid, xco.option_name, xiW.id, xiW.image_path, t1.dCount
 FROM xcart_products xp
 INNER JOIN xcart_variants xv ON xp.productid = xv.productid
 INNER JOIN xcart_variant_items xvi ON xv.variantid = xvi.variantid
 INNER JOIN xcart_class_options xco ON xvi.optionid = xco.optionid
 INNER JOIN xcart_classes xc ON xco.classid = xc.classid AND xc.class = 'COLOR'
 LEFT JOIN xcart_images_W xiW ON xiW.id = xvi.variantid

 -- since the optionId is on the thing you're counting,
 -- don't bother with any joins in the nested query and just 
 -- count and group.
 LEFT JOIN (
 SELECT xiD.optionId as optionid, count(*) as dCount 
    FROM xcart_images_D xiD
    GROUP BY xiD.optionId
 ) as t1 ON xco.optionid = t1.optionid
 -- still join the inner select based on the optionid

 GROUP BY xco.optionid
 ORDER by xp.product DESC