Question

以下是我想要执行的SQL。我想避免做多次请求，我很确定这是可能的......

First table : products_categories (category_id, category_infos…)
Second table : products_categories_relations (product_id, category_id)
Third table : products (product_id, published, products_infos…)

我想查找所有空类别（其中没有产品）和仅包含未发布产品的类别。第二部分是我被困的地方。

SELECT pc.`category_id`
FROM `#__products_categories` AS pc
LEFT JOIN `#__products_categories_relations` pcr 
ON pc.`category_id` = pcr.`category_id`
WHERE pcr.`category_id` IS NULL

此查询为我提供了没有产品的类别，但我无法看到如何插入条件说：

“对于每个带有产品的类别，返回仅包含已公布的产品= 0”的

我的分析是：
如果A是查询“没有产品的类别”的结果和B是“仅有未发布产品的类别”的结果我需要A或B中的类别。

Answer 1

SELECT pc.*
FROM products_categories pc
INNER JOIN products_categories_relations pcr
ON (pc.category_id = pcr.category_id)
INNER JOIN products p
ON (pcr.product_id = p.product_id AND published = 0)
EXCEPT
SELECT pc.*
FROM products_categories pc
INNER JOIN products_categories_relations pcr
ON (pc.category_id = pcr.category_id)
INNER JOIN products p
ON (pcr.product_id = p.product_id AND published != 0)

基本上，您查询具有已发布= 0的产品的类别，并从集合中删除所有已发布非0的产品。这将完全满足您的需求。

请注意，已发布= 0的产品的类别与空类别不同。如果您还需要空类别，只需制作union all。

编辑：正如我刚才提醒的那样，MySQL 仍然没有一些基本的SQL操作可以解决这个问题：

SELECT pc.*
FROM products_categories pc
INNER JOIN products_categories_relations pcr
ON (pc.category_id = pcr.category_id)
INNER JOIN products p
ON (pcr.product_id = p.product_id AND published = 0)
WHERE pc.product_category_id NOT IN 
(
    SELECT distinct pc.product_category_id
    FROM products_categories pc
    INNER JOIN products_categories_relations pcr
    ON (pc.category_id = pcr.category_id)
    INNER JOIN products p
    ON (pcr.product_id = p.product_id AND published != 0)
)

或者你也可以做到：

SELECT * FROM 
(
    SELECT distinct pc.*
    FROM products_categories pc
    INNER JOIN products_categories_relations pcr
    ON (pc.category_id = pcr.category_id)
    INNER JOIN products p
    ON (pcr.product_id = p.product_id AND published = 0)
) subQ1
LEFT OUTER JOIN
(
    SELECT distinct pc.*
    FROM products_categories pc
    INNER JOIN products_categories_relations pcr
    ON (pc.category_id = pcr.category_id)
    INNER JOIN products p
    ON (pcr.product_id = p.product_id AND published != 0)
) subQ2
ON subQ1.product_category_id = subQ2.product_category_id
WHERE subQ2.product_category_id IS NULL

我怀疑第一个应该更快，但你可以尝试两者。

Answer 2

UNION可能会帮到你：

SELECT pc.`category_id`
FROM `#__products_categories` AS pc
LEFT JOIN `#__products_categories_relations` pcr 
ON pc.`category_id` = pcr.`category_id`
WHERE pcr.`category_id` IS NULL
union
select category_id
from
(
SELECT pc.`category_id`,
sum(case when p.`published`=0 then 1 else 0 end) as unpublishedProductsCount,
count(*) as allProductsCount
FROM `#__products_categories` AS pc
INNER JOIN `#__products_categories_relations` pcr 
ON pc.`category_id` = pcr.`category_id`
INNER JOIN `#__products` p on p.product_id = pcr.product_id 
GROUP BY pc.`category_id`
) t
where t.allProductsCount = t.unpublishedProductsCount
;

union上方的上半部分是查询空类别的查询。

union下方的下半部分是一个查询，用于查找仅包含published=0

产品的类别

Answer 3

SELECT pc.`category_id`
FROM `#__products_categories` AS pc
LEFT JOIN `#__products_categories_relations` pcr 
ON pc.`category_id` = pcr.`category_id`
LEFT JOIN (SELECT product_id, MAX(published) published
           FROM products
           GROUP BY product_id
           HAVING published = 0) p
ON pcr.product_id = p.product_id
WHERE pcr.`category_id` IS NULL OR p.product_id IS NOT NULL

子查询查找所有未发布的产品。我们加入，然后WHERE子句可以匹配不存在的产品与第一个测试，或未发布的产品与第二个测试匹配。

硬SQL查询 - 在另一个表中没有匹配的行或在另一个表中没有发布的项

3 个答案: