Question

我第一次使用CONNECT BY命令，我理解它可以用它创建循环。我试图创建一个查询，为一个开始时间和结束时间之间的每个时间戳生成一行，具有可变间隔。当我单独为每个“路线”运行此查询时，它完美地运行。但是当我尝试同时为两个路由运行它时，循环继续。

我做错了什么？

SELECT ROUTE_NAME, START_TIME + (LEVEL - 1) * TIME_PERIOD OUTPUT_MOMENT
  FROM (SELECT *
          FROM (SELECT 1 / 24 AS TIME_PERIOD,
                       SYSDATE - 8 / 24 AS START_TIME,
                       SYSDATE + 3 / 24 AS END_TIME,
                       'ROUTE A' ROUTE_NAME
                  FROM DUAL
                UNION ALL
                SELECT 1 / 48 AS TIME_PERIOD,
                       SYSDATE - 8 / 24 AS START_TIME,
                       SYSDATE + 3 / 24 AS END_TIME,
                       'ROUTE B' ROUTE_NAME
                  FROM DUAL)
         WHERE ROUTE_NAME IN ('ROUTE A')
         --WHERE ROUTE_NAME IN ('ROUTE B')
         --WHERE ROUTE_NAME IN ('ROUTE A', 'ROUTE B')
       )
CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / TIME_PERIOD

路线A的结果：

* ROUTE_NAME    OUTPUT_MOMENT
* ROUTE A   9/3/2018 5:41:01
* ROUTE A   9/3/2018 6:41:01
* ROUTE A   9/3/2018 7:41:01
* ROUTE A   9/3/2018 8:41:01
* ROUTE A   9/3/2018 9:41:01
* ROUTE A   9/3/2018 10:41:01
* ROUTE A   9/3/2018 11:41:01
* ROUTE A   9/3/2018 12:41:01
* ROUTE A   9/3/2018 13:41:01
* ROUTE A   9/3/2018 14:41:01
* ROUTE A   9/3/2018 15:41:01

路线B上的结果：

* ROUTE_NAME    OUTPUT_MOMENT
* ROUTE B   9/3/2018 5:42:34
* ROUTE B   9/3/2018 6:12:34
* ROUTE B   9/3/2018 6:42:34
* ROUTE B   9/3/2018 7:12:34
* ROUTE B   9/3/2018 7:42:34
* ROUTE B   9/3/2018 8:12:34
* ROUTE B   9/3/2018 8:42:34
* ROUTE B   9/3/2018 9:12:34
* ROUTE B   9/3/2018 9:42:34
* ROUTE B   9/3/2018 10:12:34
* ROUTE B   9/3/2018 10:42:34
* ROUTE B   9/3/2018 11:12:34
* ROUTE B   9/3/2018 11:42:34
* ROUTE B   9/3/2018 12:12:34
* ROUTE B   9/3/2018 12:42:34
* ROUTE B   9/3/2018 13:12:34
* ROUTE B   9/3/2018 13:42:34
* ROUTE B   9/3/2018 14:12:34
* ROUTE B   9/3/2018 14:42:34
* ROUTE B   9/3/2018 15:12:34
* ROUTE B   9/3/2018 15:42:34
* ROUTE B   9/3/2018 16:12:34
* ROUTE B   9/3/2018 16:42:34

两者的结果（存在更多行）：

* ROUTE_NAME    OUTPUT_MOMENT
* ROUTE A   9/3/2018 5:43:21
* ROUTE A   9/3/2018 6:43:21
* ROUTE A   9/3/2018 7:43:21
* ROUTE A   9/3/2018 8:43:21
* ROUTE A   9/3/2018 9:43:21
* ROUTE A   9/3/2018 10:43:21
* ROUTE A   9/3/2018 11:43:21
* ROUTE A   9/3/2018 12:43:21
* ROUTE A   9/3/2018 13:43:21
* ROUTE A   9/3/2018 14:43:21
* ROUTE A   9/3/2018 15:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21
* ROUTE B   9/3/2018 13:13:21
* ROUTE B   9/3/2018 13:43:21
* ROUTE B   9/3/2018 14:13:21
* ROUTE B   9/3/2018 14:43:21
* ROUTE B   9/3/2018 15:13:21
* ROUTE B   9/3/2018 15:43:21
* ROUTE B   9/3/2018 16:13:21
* ROUTE B   9/3/2018 16:43:21
* ROUTE B   9/3/2018 10:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21
* ROUTE B   9/3/2018 13:13:21
* ROUTE B   9/3/2018 13:43:21
* ROUTE B   9/3/2018 14:13:21
* ROUTE B   9/3/2018 14:43:21
* ROUTE B   9/3/2018 15:13:21
* ROUTE B   9/3/2018 15:43:21
* ROUTE B   9/3/2018 16:13:21
* ROUTE B   9/3/2018 16:43:21
* ROUTE B   9/3/2018 10:13:21
* ROUTE A   9/3/2018 15:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21
* ROUTE B   9/3/2018 13:13:21
* ROUTE B   9/3/2018 13:43:21
* ROUTE B   9/3/2018 14:13:21
* ROUTE B   9/3/2018 14:43:21
* ROUTE B   9/3/2018 15:13:21
* ROUTE B   9/3/2018 15:43:21
* ROUTE B   9/3/2018 16:13:21
* ROUTE B   9/3/2018 16:43:21
* ROUTE B   9/3/2018 10:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21
* ROUTE B   9/3/2018 13:13:21
* ROUTE B   9/3/2018 13:43:21
* ROUTE B   9/3/2018 14:13:21
* ROUTE B   9/3/2018 14:43:21
* ROUTE B   9/3/2018 15:13:21
* ROUTE B   9/3/2018 15:43:21
* ROUTE B   9/3/2018 16:13:21
* ROUTE B   9/3/2018 16:43:21
* ROUTE B   9/3/2018 9:43:21
* ROUTE A   9/3/2018 14:43:21
* ROUTE A   9/3/2018 15:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21
* ROUTE B   9/3/2018 13:13:21
* ROUTE B   9/3/2018 13:43:21
* ROUTE B   9/3/2018 14:13:21
* ROUTE B   9/3/2018 14:43:21
* ROUTE B   9/3/2018 15:13:21
* ROUTE B   9/3/2018 15:43:21
* ROUTE B   9/3/2018 16:13:21
* ROUTE B   9/3/2018 16:43:21
* ROUTE B   9/3/2018 10:43:21
* ROUTE B   9/3/2018 11:13:21
* ROUTE B   9/3/2018 11:43:21
* ROUTE B   9/3/2018 12:13:21
* ROUTE B   9/3/2018 12:43:21

Answer 1

connect by仅基于时间，因此您每次都将路线A与路线B连接，反之亦然。

简单的解决办法似乎是：

CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / TIME_PERIOD
AND ROUTE_NAME = PRIOR ROUTE_NAME

一次将其限制为单一路线;但那后形成一个循环，所以你需要添加一个非deterministc函数调用来防止这种情况;例如：

CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / TIME_PERIOD
AND ROUTE_NAME = PRIOR ROUTE_NAME
AND PRIOR DBMS_RANDOM.VALUE() IS NOT NULL

得到：

ROUTE_NAME OUTPUT_MOMENT      
---------- -------------------
ROUTE A    2018-03-09 05:00:08
ROUTE A    2018-03-09 06:00:08
ROUTE A    2018-03-09 07:00:08
ROUTE A    2018-03-09 08:00:08
ROUTE A    2018-03-09 09:00:08
ROUTE A    2018-03-09 10:00:08
ROUTE A    2018-03-09 11:00:08
ROUTE A    2018-03-09 12:00:08
ROUTE A    2018-03-09 13:00:08
ROUTE A    2018-03-09 14:00:08
ROUTE A    2018-03-09 15:00:08
ROUTE B    2018-03-09 05:00:08
ROUTE B    2018-03-09 05:30:08
ROUTE B    2018-03-09 06:00:08
ROUTE B    2018-03-09 06:30:08
ROUTE B    2018-03-09 07:00:08
ROUTE B    2018-03-09 07:30:08
ROUTE B    2018-03-09 08:00:08
ROUTE B    2018-03-09 08:30:08
ROUTE B    2018-03-09 09:00:08
ROUTE B    2018-03-09 09:30:08
ROUTE B    2018-03-09 10:00:08
ROUTE B    2018-03-09 10:30:08
ROUTE B    2018-03-09 11:00:08
ROUTE B    2018-03-09 11:30:08
ROUTE B    2018-03-09 12:00:08
ROUTE B    2018-03-09 12:30:08
ROUTE B    2018-03-09 13:00:08
ROUTE B    2018-03-09 13:30:08
ROUTE B    2018-03-09 14:00:08
ROUTE B    2018-03-09 14:30:08
ROUTE B    2018-03-09 15:00:08
ROUTE B    2018-03-09 15:30:08
ROUTE B    2018-03-09 16:00:08

34 rows selected.

您还可以执行两个connect by查询并将结果合并在一起，可能将时间范围拉入CTE以避免重复：

WITH START_END AS (
  SELECT SYSDATE - 8 / 24 AS START_TIME,
         SYSDATE + 3 / 24 AS END_TIME
  FROM DUAL
)
SELECT 'ROUTE A' ROUTE_NAME,
       START_TIME + (LEVEL - 1) / 24 AS OUTPUT_MOMENT
  FROM START_END
CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / (1 / 24)
UNION ALL
SELECT 'ROUTE B' ROUTE_NAME,
       START_TIME + (LEVEL - 1) / 48 AS OUTPUT_MOMENT
FROM START_END
CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / (1 / 48)

使用/ ( 1 / 24)看起来很奇怪，而你可以做* 24，但实际上由于四舍五入错误，你的结果会略有不同;使用后者，您可以为路径A获得额外的行。您可以进一步重新排列逻辑以避免混淆。

Answer 2

你得到的是用层次查询的每个级别将行加倍考虑一个简单的例子：

WITH dbl AS (
    SELECT * FROM dual  UNION ALL SELECT *FROM dual
)
SELECT *FROM dbl CONNECT BY LEVEL <= N

对于N=2，查询返回6行，对于N=6，它返回126行，N=10 - 2046行。所以我们看到行号以指数方式增长。

您的查询以类似的方式工作。要解决此问题，您可以将union all移至外层，为每条路线运行单独的分层查询：

SELECT ROUTE_NAME, START_TIME + (lvl - 1) * TIME_PERIOD
FROM (
    SELECT LEVEL AS lvl, ROUTE_NAME AS "ROUTE A"... 
    ...
    FROM DUAL CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / TIME_PERIOD
)
UNION ALL 
SELECT ROUTE_NAME, START_TIME + (lvl - 1) * TIME_PERIOD
FROM (
    SELECT LEVEL AS lvl, ROUTE_NAME AS "ROUTE B", ... 
    ...
    FROM DUAL CONNECT BY (LEVEL - 1) <= (END_TIME - START_TIME) / TIME_PERIOD
)

或者使用ROUTE_NAME = PRIOR ROUTE_NAME阻止一条路线跟随另一条路线，如另一个答案所示。

Oracle SQL：CONNECT BY LEVEL返回许多行

2 个答案: