MySQL-父项的总和+；子类别

我有两张桌子：

父子“类别”：

id    name         parent_id
1     Food         NULL
2     Pizza        1
3     Pasta        2

‘交易’：

id     amount      category_id
1      100         1
2      50          2
3      25          2

我想返回所有类别以及两个总列：

总计=具有此类别id的所有交易的金额之和

parentTotal=总计+其所有子类别的总计

示例（使用上表）：

编辑：

代码已更新（基于下面Nedret Recep的代码），运行良好

SELECT 
    tmp1.id, tmp1.name, tmp1.parent_id, tmp1.total, IFNULL(tmp1.total, 0) + IFNULL(tmp2.s, 0)  AS parenttotal
   FROM
        (SELECT
                ca.id, ca.name, ca.parent_id, SUM(tr.amount) as total
        FROM
            categories ca

        LEFT JOIN
                transactions tr
        ON
                tr.category_id = ca.id 
        GROUP BY
                ca.id)
    AS tmp1     

LEFT JOIN 
        (SELECT
            c.id, c.parent_id as categoryid, SUM(t.amount) AS s  
        FROM
            transactions t
        RIGHT JOIN
            categories c
        ON
            t.category_id = c.id
        GROUP BY 
            c.parent_id)
    AS tmp2

ON tmp2.categoryid = tmp1.id 

order by coalesce(tmp1.parent_id, tmp1.id), tmp1.parent_id

---

我真的很感谢你的帮助-谢谢

通过一个内部联接，我们计算标准类别中的总数。然后，通过另一个内部联接，我们计算总和，但这次是按父对象id分组。然后，我们联接两个结果表，使两个总和在一行中。对于大型表，此查询速度较慢，因此应用程序级别的替代方法会更好

  SELECT 
        tmp1.id, tmp1.name, tmp1.parent_id, tmp1.total, tmp1.total + tmp2.s AS parenttotal
   FROM
   (SELECT
        ca.id, ca.name, ca.parent_id, SUM(tr.amount) as total
   FROM
        transactions tr
   INNER JOIN
        categories ca
   ON
        tr.categoru_id = ca.id 
   GROUP BY
        ca.id)AS tmp1     
   LEFT OUTER JOIN 
   (
   SELECT
     c.parent_id as categoryid, SUM(t.amount) AS s  
   FROM
      transactions t
   INNER JOIN
      categories c
   ON
      t.category_id = c.i
   GROUP 
       BY c.id ) AS tmp2
   ON
       tmp2.categoryid = tmp.id 

---

类别是仅在两个级别上，还是具有无限深度的树状结构？也就是说，类别比萨饼也可以有子类别。只有两级树和无限级树会有不同的方法。是的，类别只有两级深。谢谢你，我在你的基础上修改了我的答案，更新了我的代码。一切都很好。但是，如果父类别没有交易记录，则合计和父合计都返回零-即，它不会将子交易记录的合计相加。知道为什么吗？感谢您将

tmp1.total+tmp2.s

替换为

IFNULL（tmp1.total，0）+tmp2.s

IFNULL有助于将NULL转换为0，并保留值。@ginsberg:实际上您可能还需要将

IFNULL（）

应用于

tmp2.s

。谢谢大家。现在效果很好。以上代码已更新。

  SELECT 
        tmp1.id, tmp1.name, tmp1.parent_id, tmp1.total, tmp1.total + tmp2.s AS parenttotal
   FROM
   (SELECT
        ca.id, ca.name, ca.parent_id, SUM(tr.amount) as total
   FROM
        transactions tr
   INNER JOIN
        categories ca
   ON
        tr.categoru_id = ca.id 
   GROUP BY
        ca.id)AS tmp1     
   LEFT OUTER JOIN 
   (
   SELECT
     c.parent_id as categoryid, SUM(t.amount) AS s  
   FROM
      transactions t
   INNER JOIN
      categories c
   ON
      t.category_id = c.i
   GROUP 
       BY c.id ) AS tmp2
   ON
       tmp2.categoryid = tmp.id