根据条件选择查询和计数

Question

我想选择所有类别，子类别并计算属于子类别的业务数量。这是我正在使用的 SQl 查询。

SELECT
    c.id, 
    c.name,
    c.slug,
    sc.id,
    sc.name,
    sc.slug,
    COUNT(bsc.id) AS business_count
FROM 
    fi_category c
LEFT JOIN 
    fi_subcategory sc ON c.id = sc.category_id AND (sc.deleted_at IS NULL) 
LEFT JOIN 
    fi_business_subcategory bsc ON sc.id = bsc.subcategory_id AND (bsc.deleted_at IS NULL) 
WHERE 
    (c.deleted_at IS NULL) 
GROUP BY 
    c.id, sc.id

但是我想做的还有更多，应该根据他们所属的城市过滤 business_count，即最后我想选择所有类别、子类别，但 business_count 应该有一个像 WHERE city.id = 1 这样的子句，我猜我必须使用计数作为我无法弄清楚的子查询。

下面是fi_business_subcategory到fi_city的关系结构。

1) fi_business_subcategory

+----+----------------+-------------+
| id | subcategory_id | business_id |
+----+----------------+-------------+

2) fi_business

+----+---------+-----------+
| id | name    | suburb_id |
+----+---------+-----------+

3) fi_suburb

+-----+--------+---------+
| id  | name   | city_id |
+-----+--------+---------+

4) fi_city

+----+--------+
| id | name   |
+----+--------+

我尝试了类似的方法，但这似乎不起作用

SELECT
    c.id, 
    c.name,
    c.slug,
    sc.id,
    sc.name,
    sc.slug,
    bsc.business_count
FROM 
    fi_category c
LEFT JOIN 
    fi_subcategory sc ON c.id = sc.category_id AND (sc.deleted_at IS NULL) 
LEFT JOIN (
    SELECT 
        COUNT(business_id) t1.business_count, t1.subcategory_id 
    FROM
        fi_business_subcategory t1
    LEFT JOIN
        fi_business t2 ON t2.id = t1.business_id
    LEFT JOIN
        fi_suburb t3 ON t3.id = t2.suburb_id
    LEFT JOIN
        fi_city t4 ON t4.id = t3.city_id
    WHERE
        t4.id = 1
    GROUP BY
        t1.subcategory_id
) bsc ON sc.id = bsc.subcategory_id AND (bsc.deleted_at IS NULL)
WHERE 
    (c.deleted_at IS NULL) 
GROUP BY 
    c.id, sc.id

我应该如何构建查询以实现我想要的？

Answer 1

我认为您没有理由必须使用子查询。我相信您可以简单地将fi_business 和fi_business_subcategory 组合成一个带括号的表格因子。

SELECT
    c.id, 
    c.name,
    c.slug,
    sc.id,
    sc.name,
    sc.slug,
    COUNT(bsc.id) AS business_count
FROM
    fi_category c
LEFT JOIN
    fi_subcategory sc ON c.id = sc.category_id AND (sc.deleted_at IS NULL)
LEFT JOIN (
        fi_business b
    INNER JOIN
        fi_business_subcategory bsc ON b.id = bsc.business_id AND (bsc.deleted_at IS NULL)
    INNER JOIN
        fi_suburb su ON su.id = b.suburb_id AND su.city_id = 1
    ) ON sc.id = bsc.subcategory_id
WHERE 
    (c.deleted_at IS NULL) 
GROUP BY 
    c.id, sc.id

我已经checked 认为这是对您的表结构有效的 SQL。我想它很有可能会产生预期的结果，即使你的小提琴还不包含任何数据。请参阅the manual on JOIN syntax，了解有关可以在连接中使用括号的位置的详细信息。

您也可能会问自己，您是否真的需要将所有连接都保留为左连接。使用内部连接编写东西会容易得多。

由于连接是从左到右执行的，您可以先执行内部连接，然后是一系列 右 连接。这避免了括号：

SELECT
    c.id cat_id,
    c.name cat_name,
    c.slug cat_slug,
    sc.id sub_id,
    sc.name sub_name,
    sc.slug sub_slug,
    COUNT(bsc.id) AS business_count
FROM
    fi_business b
INNER JOIN
    fi_business_subcategory bsc ON b.id = bsc.business_id
    AND (b.deleted_at IS NULL) AND (bsc.deleted_at IS NULL)
INNER JOIN
    fi_suburb su ON su.id = b.suburb_id AND su.city_id = 1
RIGHT JOIN
    fi_subcategory sc ON sc.id = bsc.subcategory_id
RIGHT JOIN
    fi_category c ON c.id = sc.category_id AND (sc.deleted_at IS NULL)
WHERE
    (c.deleted_at IS NULL)
GROUP BY
    c.id, sc.id

Answer 2

如果您想使用子查询，正确的方法是用尽可能小的变化来表达您的第二个查询：

SELECT
    c.id, 
    c.name,
    c.slug,
    sc.id,
    sc.name,
    sc.slug,
    IFNULL(bsc.business_count, 0)
          -- turn NULL from left join into 0
FROM 
    fi_category c
LEFT JOIN 
    fi_subcategory sc ON c.id = sc.category_id AND (sc.deleted_at IS NULL) 
LEFT JOIN (
    SELECT 
        COUNT(*) business_count, t1.subcategory_id
          -- removed table name from alias name,
          -- and improved performance by simply counting rows
    FROM
        fi_business_subcategory t1
    LEFT JOIN
        fi_business t2 ON t2.id = t1.business_id
    LEFT JOIN
        fi_suburb t3 ON t3.id = t2.suburb_id
    LEFT JOIN
        fi_city t4 ON t4.id = t3.city_id
    WHERE
        t4.id = 1 AND (t1.deleted_at IS NULL)
          -- check deletion in subquery for performance
    GROUP BY
        t1.subcategory_id
) bsc ON sc.id = bsc.subcategory_id
          -- no longer need to check deletion here
WHERE 
    (c.deleted_at IS NULL) 
GROUP BY 
    c.id, sc.id

小提琴here.

Answer 3

试试这个

select 
    c.id,
    c.name,
    count(sc.name) as Count
from fi_category as c
left join fi_subcategory as sc on sc.category_id = c.id
left join fi_business_subcategory as  fbs on fbs.subcategory_id = sc.id
inner join (
select 
    fb.name,
    fs.id,
    fs.city_id

from fi_business as fb 
inner join fi_suburb as fs on fs.id = fb.suburb_id
where fs.city_id = 1



) as  fb on fb.id = fbs.business_id
group by c.id