分層查詢最多3次自聯接表

Question

我有一個帶有以下各列的表的Oracle DB：

    ID | PARENTID | DETAIL1
    ------------------------
    1  | NULL     | BLAH1
    2  | 1        | BLAH2
    3  | 2        | BLAH3
    4  | 2        | BLAH4
    5  | NULL     | BLAH5
    6  | 5        | BLAH6
    7  | 6        | BLAH7
    8  | 5        | BLAH8
    9  | 5        | BLAH9
    10 | 8        | BLAH10

我准備了一個自我加入

    SELECT    PARENT.ID AS "PID",
              PARENT.DETAIL1 AS "PDETAIL1",
              CHILD.ID AS "CID",
              CHILD.DETAIL1 AS "CDETAIL1" 

      FROM    table1 CHILD

      LEFT OUTER JOIN table1 PARENT

      ON      PARENT.ID = CHILD.PARENTID
      WHERE   PARENTID IS NOT NULL;

輸出如下所示：

    PID | PDETAIL1 | CID | CDETAIL1|
    --------------------------------
    1   | BLAH1    | 2   | BLAH2   |
    2   | BLAH2    | 3   | BLAH3   |
    2   | BLAH2    | 4   | BLAH4   |
    5   | BLAH5    | 6   | BLAH6   |
    6   | BLAH6    | 7   | BLAH7   |
    5   | BLAH5    | 8   | BLAH8   |
    5   | BLAH5    | 9   | BLAH9   |
    8   | BLAH8    | 10  | BLAH10  |

非常簡單。 我想知道是否可以將這種自我聯接作為層次/遞歸查詢來完成。 最大嵌套深度為3。目標輸出應如下所示：

    GPID | GPDETAIL1 | PID | PDETAIL1 | CID  | CDETAIL1 |
    ---------------------------------------------------
    1    | BLAH1     | 2   | BLAH2    | 3    | BLAH3    |
    1    | BLAH1     | 2   | BLAH2    | 4    | BLAH4    |
    5    | BLAH5     | 6   | BLAH6    | 7    | BLAH7    |
    5    | BLAH5     | 8   | BLAH8    | 10   | BLAH10   |
    5    | BLAH5     | 9   | BLAH9    | NULL | NULL     |

Google並沒有幫助我，有大量與分層查詢有關的信息，但是沒有任何信息（包括自我聯接和分層查詢），而且大多數問題在表面上看起來都是相似的，但是沒有什么可以指導我滿足我的需求。 我是SQL新手，因此，除非答案是特定的，否則我可能會錯過它。

Answer 1

您只需要再join一次餐桌就可以得到孩子們。 因此，基本上有一個祖父母別名，父別名和子別名，並相應地join ：

select 
    gp.id as gpid,
    gp.detail as gpdetail1,
    p.id as pid,
    p.detail as pdetail1,
    c.id as cid,
    c.detail as cdetail1
from yourtable gp
    left join yourtable p on gp.id = p.parentid
    left join yourtable c on p.id = c.parentid
where gp.parentid is null

• SQL小提琴演示

Answer 2

有大量與分層查詢有關的信息，但沒有任何信息包括自我聯接和分層查詢

您不需要兩者，層次查詢是自連接。

您可以從類似於以下的分層查詢開始：

select connect_by_root (id) as gpid, connect_by_root(detail1) as gpdetail1,
  prior id as pid, prior detail1 as pdetail1,
  id as cid, detail1 as cdetail1,
  level as lvl, connect_by_isleaf as is_leaf
from table1
start with parentid is null
connect by prior id = parentid

請參閱文檔 ，了解connect_by_root和connect_by_isleaf的含義。 您對葉節點感興趣，但是：

select *
from (
  select connect_by_root (id) as gpid, connect_by_root(detail1) as gpdetail1,
    prior id as pid, prior detail1 as pdetail1,
    id as cid, detail1 as cdetail1,
    level as lvl, connect_by_isleaf as is_leaf
  from table1
  start with parentid is null
  connect by prior id = parentid
)
where is_leaf = 1;

...沒有得到您想要的東西：

      GPID GPDETA        PID PDETAI        CID CDETAI        LVL    IS_LEAF
---------- ------ ---------- ------ ---------- ------ ---------- ----------
         1 BLAH1           2 BLAH2           3 BLAH3           3          1
         1 BLAH1           2 BLAH2           4 BLAH4           3          1
         5 BLAH5           6 BLAH6           7 BLAH7           3          1
         5 BLAH5           8 BLAH8          10 BLAH10          3          1
         5 BLAH5           5 BLAH5           9 BLAH9           2          1

從示例輸出中，您不希望在最后一行的父列中使用5 / BLAH5，因為它們是祖父母。 您希望將子級值提升為父級狀態。 不過，您可以稍微操縱父級和子級值：

select gpid, gpdetail1,
  case lvl when 2 then cid else pid end as pid,
  case lvl when 2 then cdetail1 else pdetail1 end as pdetail1,
  case lvl when 2 then null else cid end as cid,
  case lvl when 2 then null else cdetail1 end as cdetail1
from (
  select connect_by_root (id) as gpid, connect_by_root(detail1) as gpdetail1,
    prior id as pid, prior detail1 as pdetail1,
    id as cid, detail1 as cdetail1,
    level as lvl, connect_by_isleaf as is_leaf
  from table1
  start with parentid is null
  connect by prior id = parentid
)
where is_leaf = 1;

      GPID GPDETA        PID PDETAI        CID CDETAI
---------- ------ ---------- ------ ---------- ------
         1 BLAH1           2 BLAH2           3 BLAH3 
         1 BLAH1           2 BLAH2           4 BLAH4 
         5 BLAH5           6 BLAH6           7 BLAH7 
         5 BLAH5           8 BLAH8          10 BLAH10
         5 BLAH5           9 BLAH9                   

但是只有三個固定級別，再次加入更加容易理解...