如何使用多个选择查询优化 UNION mysql 查询？

Question

我要求在产品详细信息页面中显示类似产品，以便列出的产品应以分层方式与当前产品属性匹配，如下所示

1. 尺寸、颜色、类别、公司应与当前产品匹配
2. 尺寸、颜色、类别应与当前产品匹配
3. 尺寸、颜色应与当前产品相匹配
4. 尺寸应与当前产品匹配

我的sql查询如下：

(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 - 当前产品 ID 和状态表示可用！

有没有办法优化上面的查询？

需要备注输出：我们需要 10 个类似的产品。如果有 4 个符合条件 1 的产品，则需要先随机列出。同样，我们需要在其下方列出符合其他条件的产品。

提前致谢！

Answer 1

继续使用 ORDER BY RAND()（效率不高）然后一个非常基本的改进是为每个子句添加一个优先级，将 order 子句移到最后，因此只需要它一次。

(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 

然后可以通过以下方式在不需要工会的情况下完成：-

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