MySQL 每个父母及其子女的返回列表答案

【问题标题】：MySQL return list of each parent and its childrenMySQL 每个父母及其子女的返回列表
【发布时间】：2018-05-16 22:04:48
【问题描述】：

我有一张如下表：

Manager 是父级，其下的子资源与经理的父级 ID 相连。

id    | parent_id   |   Role       | Number of roles

123   | 123         | Manager      |    2

124   | 123         | Resource     |    1

125   | 123         | Resource     |    2

128   | 128         | Manager      |    1

126   | 128         | Resource     |    4

127   | 128         | Resource     |    3

我的 sql 查询应该为每个父级返回以下结果：

id    | parent_id   |   Role       | Sum of manager only | Total resources

123   | 123         | Manager      |    2                |    2+1+2 = 5 (Manager + the total number of resources for parent id 123)   

128   | 128         | Manager      |    1                |    1+4+3 = 8 (Manager + the total number of resources for parent id 128)

任何帮助将不胜感激。谢谢。

【问题讨论】：

子查询应该是最后一个选项，因为它会降低您的系统速度。

标签： mysql sql plsql mysql-workbench recursive-query

【解决方案1】：

我希望这样做：

SELECT 
    m1.*, m2.sum_roles
FROM
    managers_workers m1
        LEFT JOIN
    (SELECT 
        parent_id, SUM(num_of_roles) AS sum_roles
    FROM
        managers_workers
    GROUP BY parent_id) AS m2 ON m1.id = m2.parent_id
WHERE
    m2.parent_id IS NOT NULL
;

【讨论】：

【解决方案2】：

您只需要使用父 ID 进行自我加入。如果你的表名是“tbl_manager”

SELECT t1.id,
    SUM(IF(t1.id = t2.id, 1,0)) AS is_manager,
    t1.parent_id, 
    t1.Role, 
    t1.Number_of_Role AS Sum_of_manager_only,
    IFNULL(SUM(t2.Number_of_Role),0) AS Total_resources 
FROM  tbl_manager AS t1 
LEFT JOIN  tbl_manager AS t2 
    ON t2.parent_id = t1.id 
GROUP BY t1.id
HAVING is_manager;

【讨论】：

【解决方案3】：

你可以使用子查询

select
    (select id from mytbl where id=r.parent_id)  id
    ,r.parent_id
    ,(select sum(NofRole) from mytbl where parent_id=r.parent_id and Role='Manager') [Sum of manager only]
    , sum(r.nofrole) [Total resources]
    from mytbl r
    group by r.parent_id

【讨论】：