可以在条件中使用分层查询吗？

Question

我将使用分层查询在 Oracle Forms 中构建一个分层树。据我所知，HQ 仅适用于单个 table，是否可以在我们有 Master Details 场景的情况下使用它们。

还是可以基于视图？

例如；我想显示一个层次结构，其中包含来自各种 table 的 3 个选项。例如，客户订单可以有各种项目。所有 CO 的第一个列表，单击特定 CO，其中的所有项目，一个项目可能有子部分，等等。跨越多个连接 tables

Answer 1

如果你有测试数据：

CREATE TABLE customer_orders ( id, name ) AS
SELECT 1, 'Cust. Ord. XYZ' FrOM DUAL UNION ALL
SELECT 2, 'Cust. Ord. ABC' FrOM DUAL UNION ALL
SELECT 3, 'Cust. Ord. MNO' FrOM DUAL;

CREATE TABLE customer_order_items ( id, order_id, name ) AS
SELECT 1, 3, 'MNO_NNN' FROM DUAL UNION ALL
SELECT 2, 3, 'MNO_OOO' FROM DUAL UNION ALL
SELECT 3, 3, 'MNO_MMM' FROM DUAL UNION ALL
SELECT 4, 2, 'ABC_AAA' FROM DUAL;

CREATE TABLE customer_order_item_parts ( id, item_id, name ) AS
SELECT 1, 1, 'Part_2_N' FROM DUAL UNION ALL
SELECT 2, 1, 'Part_1_N' FROM DUAL UNION ALL
SELECT 3, 2, 'Part_1_O' FROM DUAL UNION ALL
SELECT 4, 2, 'Part_3_O' FROM DUAL UNION ALL
SELECT 5, 4, 'Part_5_A' FROM DUAL UNION ALL
SELECT 6, 4, 'Part_3_A' FROM DUAL UNION ALL
SELECT 7, 4, 'Part_2_A' FROM DUAL UNION ALL
SELECT 8, 4, 'Part_4_A' FROM DUAL;

然后您可以使用 UNION ALL（根据需要使用 JOINs）连接数据，一旦全部编译完成，您就可以应用分层查询：

SELECT *
FROM   (
  SELECT id AS order_id,
         NULL AS item_id,
         NULL AS part_id,
         name
  FROM   customer_orders
  UNION ALL
  SELECT order_id,
         id,
         NULL,
         name
  FROM   customer_order_items
  UNION ALL
  SELECT i.order_id,
         p.item_id,
         p.id,
         p.name
  FROM   customer_order_items i
         INNER JOIN
         customer_order_item_parts p
         ON ( i.id = p.item_id )
)
START WITH item_id IS NULL
CONNECT BY NOCYCLE
      PRIOR order_id = order_id
AND   (  (   PRIOR item_id IS NULL
         AND part_id IS NULL )
      OR (   PRIOR part_id IS NULL
         AND part_id IS NOT NULL
         AND PRIOR item_id = item_id )
      )
ORDER SIBLINGS BY name

输出：

ORDER_ID | ITEM_ID | PART_ID | NAME          
-------: | ------: | ------: | :-------------
       2 |    null |    null | Cust. Ord. ABC
       2 |       4 |    null | ABC_AAA       
       2 |       4 |       7 | Part_2_A      
       2 |       4 |       6 | Part_3_A      
       2 |       4 |       8 | Part_4_A      
       2 |       4 |       5 | Part_5_A      
       3 |    null |    null | Cust. Ord. MNO
       3 |       3 |    null | MNO_MMM       
       3 |       1 |    null | MNO_NNN       
       3 |       1 |       2 | Part_1_N      
       3 |       1 |       1 | Part_2_N      
       3 |       2 |    null | MNO_OOO       
       3 |       2 |       3 | Part_1_O      
       3 |       2 |       4 | Part_3_O      
       1 |    null |    null | Cust. Ord. XYZ

db<>fiddle here

可以在条件中使用分层查询吗？

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