Question

我有一个带有以下列的表的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

我为

准备了一个自我加入

    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;

输出如下所示：

    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  |

非常直接。我想知道这种自联接是否可以作为分层/递归查询来完成。最大嵌套深度为3.目标输出应如下所示：

    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     |

谷歌并没有帮助我，有大量与分层查询有关的信息，但没有任何内容包括自联接和分层查询，大多数问题看似相似（表面上看），但没有任何指导我的内容需要。我是一个SQL新手，所以除非答案是具体的，否则我可能会错过它。

Answer 1

你需要再次join到桌子上才能找到孩子。因此，基本上有一个祖父母别名，父别名和子别名，并join相应地：

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 Fiddle Demo

Answer 2

有大量与分层查询相关的信息，但不包括自连接和分层查询

您不需要两者，分层查询是自我加入。

您可以通过以下分层查询开始：

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

See the docs表示connect_by_root和connect_by_isleaf的含义。您对叶节点感兴趣，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;

......并没有得到你想要的东西：

      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

从您的示例输出中，您不想在最后一行的父列中使用5 / BLAH5，因为他们是祖父母;您希望将子值提升为父级状态。您可以稍微操纵父值和子值：

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

但只有三个固定级别再次加入更容易理解......

自连接表的分层查询最多3次

2 个答案: