mysql - 如何添加计数和清理/简化涉及 4 个 INNER JOIN 和 2 个 LEFT JOIN 的派生查询

Question

我对 MySQL 的派生查询不熟悉，并且在两件事上遇到了麻烦。

1) 如何引用 t1.dCount 以便计算每个 optionId 的 xcart_images_D.productId 数量？

2) 如何简化此查询的派生 SELECT？ (目前此查询需要 45 秒才能运行)

 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

这是计数的工作版本，但没有派生选择 -

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

如果需要，这里是数据库布局 -

+ 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

这是您的原始查询，其中包含一些描述我认为问题所在的注释:

 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

尝试如下:

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

为了加快速度，这可能会起作用，具体取决于您正在寻找的结果:

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