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

然而，我想要做的更多，business_count应该根据他们所属的城市进行过滤，即最后我想要选择所有类别，子类别但是business_count应该有一个像WHERE city.id = 1这样的子句，对于这个我我想我必须使用count作为子查询，这是我无法弄清楚的。

以下是从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   |
+----+--------+

我试过这样的事情，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目标？

Answer 1

我认为你不应该使用子查询。我相信您只需将fi_business和fi_business_subcategory合并为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checked这是您的表结构的有效SQL。我想即使你的小提琴不包含任何数据，它也会产生预期的结果。有关在联接中可以使用括号的位置的详细信息，请参阅the manual on JOIN syntax。

您可能也会问自己是否真的需要所有联接才能保留联接。使用内连接编写内容会容易得多。

当连接从左向右执行时，您可以先执行内连接，然后执行一系列右连接。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，那么使用尽可能小的变化来表达第二个查询的正确方法是：

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

根据条件选择查询和计数

3 个答案: