Oracle SQL-从单行的列组合中派生多行

Question

我在Oracle SQL DB上有这种数据：

personId  lastEvent currentEvent nextEvent
1         null      1            2
1         1         2            3
1         2         3            4
1         3         4            null

对于像这样的单行

personId  lastEvent currentEvent nextEvent
1         null      1            2

我想提取通过合并事件列并将这两行分类为特定currentEvent而提取的两行。 例如：

第1行

personId  lastEvent currentEvent nextEvent
1         null      1            2

结果1

personId  event1 event2 currentEvent
1         null   1      1
1         1      2      1  

第2行

personId  lastEvent currentEvent nextEvent
1         1         2            3

结果＃2

personId  event1 event2 currentEvent
1         1      2      2
1         2      3      2

等等。...我知道CONNECT BY子句的存在，但我真的无法弄清楚查询以获得这些结果。

Answer 1

这是执行此操作的一种方法。

我没有为此使用层次查询。

create table t(personId int,lastEvent int, currentEvent int, nextEvent int);

insert into t values(1,null,1,2);
insert into t values(1,1,2,3);
insert into t values(1,2,3,4);
insert into t values(1,3,4,null);


    select a.personId,case when b.rn=1 then 
                            a.lastEvent 
                       else a.currentEvent
                   end as event1
       ,case when b.rn=1 then 
                  a.currentEvent 
             else a.nextEvent
         end as event2
       ,case when a.nextEvent is not null then 
                  a.currentEvent
        end as currentEvent       
  from t a
  join (select rownum as rn from all_objects where rownum<=2) b
    on case when a.nextEvent is not null then 2
            else 1
        end >=b.rn
order by 1,4,3   


+----------+--------+--------+--------------+
| PERSONID | EVENT1 | EVENT2 | CURRENTEVENT |
+----------+--------+--------+--------------+
|        1 |     -  |      1 |            1 |
|        1 |      1 |      2 |            1 |
|        1 |      1 |      2 |            2 |
|        1 |      2 |      3 |            2 |
|        1 |      2 |      3 |            3 |
|        1 |      3 |      4 |            3 |
|        1 |      3 |      4 |           -  |
+----------+--------+--------+--------------+

Answer 2

这根本不是分层查询：您只想将每个输入行拆分为两个输出行并应用一些逻辑。

执行拆分的一种简单方法是将表CROSS JOIN到正好有两行的行源。

例如，

with input_data ( personId,  lastEvent, currentEvent, nextEvent) AS
(
SELECT 1, null, 1, 2     FROM DUAL UNION ALL
SELECT 1, 1,    2, 3     FROM DUAL UNION ALL
SELECT 1, 2,    3, 4     FROM DUAL UNION ALL
SELECT 1, 3,    4, null  FROM DUAL )
SELECT personId,
       decode(rn, 1, lastEvent, 2, currentEvent) event1,
       decode(rn, 1, currentEvent, 2, nextEvent) event2,
       currentEvent
from input_data 
CROSS JOIN ( SELECT rownum rn FROM DUAL CONNECT BY ROWNUM <= 2 ) r
ORDER BY personId, currentEvent, rn;

 +----------+--------+--------+--------------+ | PERSONID | EVENT1 | EVENT2 | CURRENTEVENT | +----------+--------+--------+--------------+ | 1 | | 1 | 1 | | 1 | 1 | 2 | 1 | | 1 | 1 | 2 | 2 | | 1 | 2 | 3 | 2 | | 1 | 2 | 3 | 3 | | 1 | 3 | 4 | 3 | | 1 | 3 | 4 | 4 | | 1 | 4 | | 4 | +----------+--------+--------+--------------+