递归WITH查询在oracle中如何工作？什么时候进入循环？

Question

我有一个场景，我必须根据其数量列中的值显示一行 'n' 次。

Item       Qty
abc        2 
cde        1

Item       Qty
abc        1
abc        1
cde        1

我希望将第一个 table 转换为第二个。

我发现了我应该使用递归 WITH 查询的网站。

我的主播会员returns原table.

SELECT ITEM, QTY
           FROM lines
          WHERE     
                JOB = TO_NUMBER ('1')
                AND ITEM IN
                       (SELECT PART
                          FROM PICK
                         WHERE DELIVERY = '2')

我的递归成员如下

SELECT CTE.ITEM, (CTE.QTY - 1) QTY
           FROM CTE
                INNER JOIN
                (SELECT ITEM, QTY
                   FROM LINES
                  WHERE JOB_ID = TO_NUMBER ('1')
                        AND ITEM IN
                               (SELECT PART
                                  FROM PICK
                                 WHERE DELIVERY = '2'
                                       )) T
                   ON CTE.ITEM = T.ITEM
          WHERE CTE.QTY > 1

我的目标是先获取所有零件和数量，然后在递归步骤中为所有数量 > 1 的零件生成要添加到原始结果集中的新行，新行中显示的数量将是（该部分的原始数量 - 1）。递归将继续进行，直到所有部分的 qty 变为 1。

这就是我最后的结果。

WITH CTE (ITEM, QTY)
AS (
SELECT ITEM, QTY
           FROM lines
          WHERE     
                JOB = TO_NUMBER ('1')
                AND ITEM IN
                       (SELECT PART
                          FROM PICK
                         WHERE DELIVERY = '2')
UNION ALL
SELECT CTE.ITEM, (CTE.QTY - 1) QTY
           FROM CTE
                INNER JOIN
                (SELECT ITEM, QTY
                   FROM LINES
                  WHERE JOB_ID = TO_NUMBER ('1')
                        AND ITEM IN
                               (SELECT PART
                                  FROM PICK
                                 WHERE DELIVERY = '2'
                                       )) T
                   ON CTE.ITEM = T.ITEM
          WHERE CTE.QTY > 1)
  SELECT ITEM, QTY
    FROM CTE
ORDER BY 1, 2 DESC

当我尝试上述操作时出现以下错误 "ORA-32044: cycle detected while executing recursive WITH query"

怎么进入循环的？我在它的工作中错过了什么？

此外，如果我使用 "cycle clause" 从另一个网站阅读。我能够停止循环。

我使用的子句是。

       CYCLE  
       QUANTITY   
       SET                                    
       END TO '1'                               
       DEFAULT '0'

如果我在 select 语句之前使用它。我得到了想要的输出，但我觉得这不是正确的方法。子句到底在做什么？什么是正确的使用方法？

Answer 1

Oracle 设置:

CREATE TABLE lines ( Item, Qty ) AS
SELECT 'abc', 2 FROM DUAL UNION ALL 
SELECT 'cde', 1 FROM DUAL;

CREATE TABLE pick ( part, delivery ) AS
SELECT 'abc', 2 FROM DUAL UNION ALL
SELECT 'cde', 2 FROM DUAL;

查询 1：使用分层查询：

SELECT Item,
       COLUMN_VALUE AS qty
FROM   lines l
       CROSS JOIN
       TABLE(
         CAST(
           MULTISET(
             SELECT 1
             FROM   DUAL
             CONNECT BY LEVEL <= l.Qty
           )
           AS SYS.ODCINUMBERLIST
         )
       ) t
WHERE  item IN ( SELECT part FROM pick WHERE delivery = 2 )

查询 2：使用递归子查询分解子句：

WITH rsqfc ( item, qty ) AS (
  SELECT item, qty
  FROM   lines l
  WHERE  item IN ( SELECT part FROM pick WHERE delivery = 2 )
UNION ALL
  SELECT item, qty - 1
  FROM   rsqfc
  WHERE  qty > 1
)
SELECT item, 1 AS qty
FROM   rsqfc;

输出:

ITEM | QTY
:--- | --:
abc  |   1
abc  |   1
cde  |   1

db<>fiddle here

递归WITH查询在oracle中如何工作？什么时候进入循环？

How does the recursive WITH query work in oracle? When does it go into a cycle?

oracle

recursion

cycle

recursive-query