返回 MySQL LEFT JOIN 查詢（表自連接）中的所有行

Question

我在 MySQL 8 中有以下分層表結構“ nato ”：

INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (1, NULL, 0, 'Charlie', 1);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (2, NULL, 0, 'Echo', 1);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (3, 1, 1, 'Alpha', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (4, 1, 1, 'Tango', 1);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (5, 2, 1, 'Papa', 1);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (6, 1, 1, 'Foxtrot', 1);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (7, NULL, 0, 'Uniform', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (8, 2, 1, 'Lima', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (9, 4, 2, 'Sierra', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (10, 5, 2, 'Juliet', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (11, 6, 2, 'India', 0);
INSERT INTO `nato`(`id`, `parentID`, `level`, `name`, `has_children`) VALUES (12, 6, 2, 'Oscar', 0);

（我有什么：）

id   parentID    level    name        has_children
1     (null)       0      Charlie           1
2     (null)       0      Echo              1
3         1        1      Alpha             0
4         1        1      Tango             1
5         2        1      Papa              1
6         1        1      Foxtrot           1
7     (null)       0      Uniform           0
8         2        1      Lima              0
9         4        2      Sierra            0
10        5        2      Juliet            0
11        6        2      India             0
12        6        2      Oscar             0

我正在針對它運行以下查詢，其中 L0 是 0 級等：（我嘗試了什么：）

SELECT f.id    AS L0_id,
       f.NAME  AS L0_name,
       f1.id   AS L1_id,
       f1.NAME AS L1_name,
       f2.id   AS L2_id,
       f2.NAME AS L2_name
FROM   nato f
LEFT JOIN nato f1
    ON f1.parentID = f.id
LEFT JOIN nato f2
    ON f2.parentID = f1.id
WHERE  f.parentID IS NULL
ORDER  BY l0_id ASC 

獲得跨級別“L0”到“L2”的結果：（我得到了什么：）

L0_id       L0_name     L1_id     L1_name     L2_id     L2_name
  1         Charlie       3       Alpha        (null)   (null)
  1         Charlie       4       Tango         9       Sierra
  1         Charlie       6       Foxtrot       11      India
  1         Charlie       6       Foxtrot       12      Oscar
  2         Echo          5       Papa          10      Juliet
  2         Echo          8       Lima         (null)   (null)
  7         Uniform    (null)     (null)       (null)   (null)

我希望獲得的是每個帶有孩子的項目的一行（類似於 Uniform 的行），以 id 的遞增順序，即（我期望得到的）

L0_id       L0_name     L1_id     L1_name     L2_id     L2_name
  1         Charlie     (null)    (null)       (null)   (null)
  1         Charlie       3       Alpha        (null)   (null)
  1         Charlie       4       Tango        (null)   (null)
  1         Charlie       4       Tango         9       Sierra
  1         Charlie       6       Foxtrot      (null)   (null)
  1         Charlie       6       Foxtrot       11      India
  1         Charlie       6       Foxtrot       12      Oscar
  2         Echo        (null)     (null)       (null)   (null)
  2         Echo          4       Papa         (null)   (null)
  2         Echo          5       Papa          10      Juliet
  2         Echo          8       Lima         (null)   (null)
  7         Uniform    (null)     (null)       (null)   (null)

如何修改我的查詢以實現上述結果？ 如果這會使事情變得更容易，我已經添加了兩列（ level和has_children ），但我仍然不確定如何實現我的目標。 提前致謝。

Answer 1

這是我最終使用兩個 UNION 拼湊出來的。 很可能不是最有效的方法，但我希望它對其他人有所幫助。

SELECT
        f.id as L_id,
        f.name as L_name,
        f1.id as L1_id,
        f1.name as L1_name,
        f2.id as L2_id,
        f2.name as L2_name
FROM
        nato f
LEFT JOIN nato f1
        ON f1.parentID = f.id
LEFT JOIN nato f2
        ON f2.parentID = f1.id
WHERE
        f.parentID IS NULL
UNION
   SELECT f.id as L_id,
            f.name as L_name,
            NULL as L1_id,
            NULL as L1_name,
            NULL as L2_name,
            NULL as L2_name
        FROM nato f
                 WHERE f.parentID IS NULL
                 AND f.has_children = 1
UNION
   SELECT f.id as L_id,
            f.name as L_name,
            f1.id as L1_id,
            f1.name as L1_name,
            NULL as L2_name,
            NULL as L2_name
        FROM nato f
        LEFT JOIN nato f1
             ON f1.parentID = f.id
                 WHERE f.parentID IS NULL
                 AND f1.has_children = 1
ORDER BY
        L_id,L1_id,L2_id ASC

產生預期的結果：

L_id       L_name     L1_id     L1_name     L2_id     L2_name
  1         Charlie     (null)    (null)       (null)   (null)
  1         Charlie       3       Alpha        (null)   (null)
  1         Charlie       4       Tango        (null)   (null)
  1         Charlie       4       Tango         9       Sierra
  1         Charlie       6       Foxtrot      (null)   (null)
  1         Charlie       6       Foxtrot       11      India
  1         Charlie       6       Foxtrot       12      Oscar
  2         Echo        (null)     (null)       (null)   (null)
  2         Echo          4       Papa         (null)   (null)
  2         Echo          5       Papa          10      Juliet
  2         Echo          8       Lima         (null)   (null)
  7         Uniform    (null)     (null)       (null)   (null)