代码之家 › 专栏 › 技术社区 › Matthias Günter

分层获取所有父级,无需使用CTE查询

hierarchy sql mysql

Matthias Günter · 技术社区 · 8 年前

介绍

有很多答案很好地解释了如何从父子关系中读取分层数据。我使用的是mySQL,我创建了一个查询,可以读取所有的父对象( parent_id )(通过逗号连接)对于给定的 id

create table `menu` (
    `id` double ,
    `title` varchar (765),
    `controller` varchar (765),
    `method` varchar (765),
    `url` varchar (765),
    `parent_id` varchar (765),
    `added_date` datetime ,
    `updated_date` datetime 
);

http://sqlfiddle.com/#!9/48d276f/171 . 应运行查询 无热膨胀系数

SELECT GROUP_CONCAT(T2.id) AS parents
FROM (
    SELECT
        @r AS _id,
        (SELECT @r := parent_id FROM menu WHERE id = _id) AS parent_id,
        @l := @l + 1 AS lvl
    FROM (SELECT @r := 31, @l := 0) vars, menu m
    WHERE @r <> 0) T1
JOIN menu T2
ON T1._id = T2.id
ORDER BY T1.lvl DESC;

查询结果为:

parents
-------------
3,17,31

挑战:

倍数 身份证件 我以为子查询会有帮助,但我得到了一个错误( Unknown table 'T3' in field list

预期结果应为:

id      | parents
-----------------------
25      | 5,25
31      | 3,17,31
23      | 4,23

使用的查询( http://sqlfiddle.com/#!9/48d276f/180 ):

SELECT T3.id, T4.parents
FROM menu T3, (SELECT T3.id, GROUP_CONCAT(T2.id) AS parents
  FROM (
      SELECT
          @r AS _id,
          (SELECT @r := parent_id FROM menu WHERE id = _id) AS parent_id,
          @l := @l + 1 AS lvl
      FROM (SELECT @r := T3.id, @l := 0) vars, menu m
      WHERE @r <> 0) T1
  JOIN menu T2
  ON T1._id = T2.id
  ORDER BY T1.lvl DESC) T4
WHERE T3.id IN (25, 31, 23)

1 回复 | 直到 8 年前

Solarflare 8 年前

通过使用另一个连接,您可以应用与单个id相同的逻辑,因此基本上会多次重复该计算。由于不能再使用固定的开始值,我对条件进行编码,以重新初始化交叉连接中的变量(“reset\u r”)。

请尝试以下操作:

SELECT t1.id, GROUP_CONCAT(t1.r ORDER BY t1.lvl DESC) AS parents
FROM (
  SELECT
    t0.r_init AS id, 
    @r := IF(t0.reset_r = 1, t0.r_init, 
              (select parent_id from menu where id = @r)) AS r,
    @l := IF(t0.reset_r = 1, 1, @l + 1) AS lvl
  FROM 
    (SELECT m0.id as counter, m1.id AS r_init,
       ((SELECT min(id) FROM menu) = m0.id) AS reset_r 
     FROM menu m0, menu m1
     WHERE m1.id IN (25, 31, 23)
    ) t0 
  ORDER BY t0.r_init, t0.counter
) t1
WHERE t1.r <> 0
-- or instead of "where":
-- JOIN menu t2 ON t2.id = t1.r;
GROUP BY t1.id;

对于大型表,您应该限制 p different data model . 此外,尽管您的表结构可能是一个示例,但您显然应该使用主键(否则父项和重置条件定义不明确)和相同的数据类型 parent_id 和 id

使现代化 :MySQL 5.6查询的一个版本(应该可以在 sql-fiddle

SELECT t2.id, GROUP_CONCAT(t2.r ORDER BY t2.lvl DESC)
FROM (
  SELECT id, r, lvl
  FROM (
    SELECT
      t0.r_init AS id,
      @r := IF(t0.reset_r = 1, t0.r_init, 
                (select parent_id from menu where id = @r)) AS r,
      @l := IF(t0.reset_r = 1, 1, @l + 1) AS lvl
    FROM 
      (SELECT m0.id as counter, m1.id AS r_init,
         ((SELECT min(id) FROM menu) = m0.id) AS reset_r 
       FROM menu m0, menu m1
       WHERE m1.id IN (25, 31, 23)
       ORDER BY r_init, counter
      ) t0 
    ORDER BY t0.r_init, t0.counter
  ) t1
  WHERE r <> 0
) t2
GROUP BY t2.id;