Oracle SQL查询(分析？)

Question

我正在尝试构建一个查询,以便从前一个匹配的行构建一些列.例如,使用以下数据:

CREATE TABLE TEST (SEQ NUMBER, LVL NUMBER, DESCR VARCHAR2(10));
INSERT INTO TEST VALUES (1, 1, 'ONE');
INSERT INTO TEST VALUES (2, 2, 'TWO1');
INSERT INTO TEST VALUES (3, 2, 'TWO2');
INSERT INTO TEST VALUES (4, 3, 'THREE1');
INSERT INTO TEST VALUES (5, 2, 'TWO3');
INSERT INTO TEST VALUES (6, 3, 'THREE2');
COMMIT

我想要检索以下数据.

SEQ L1  L2   L3
1   ONE NULL NULL
2   ONE TWO1 NULL
3   ONE TWO2 NULL
4   ONE TWO2 THREE1
5   ONE TWO3 THREE1
5   ONE TWO3 THREE2

即对于第3行,它本身具有L2的值,对于L1,它必须转到包含L1数据的最新行,在这种情况下是第一行.

我曾尝试查看分析和连接子句,但无法理解解决方案.
有任何想法吗？

Answer 1

更新:有一个比我的第一个答案简单得多的解决方案.它更具可读性和更优雅,因此我首先将它放在这里(通常,感谢Tom Kyte):

SQL> SELECT seq,
  2         last_value(CASE
  3                       WHEN lvl = 1 THEN
  4                        descr
  5                    END IGNORE NULLS) over(ORDER BY seq) L1,
  6         last_value(CASE
  7                       WHEN lvl = 2 THEN
  8                        descr
  9                    END IGNORE NULLS) over(ORDER BY seq) L2,
 10         last_value(CASE
 11                       WHEN lvl = 3 THEN
 12                        descr
 13                    END IGNORE NULLS) over(ORDER BY seq) L3
 14    FROM TEST;

       SEQ L1         L2         L3
---------- ---------- ---------- ----------
         1 ONE                   
         2 ONE        TWO1       
         3 ONE        TWO2       
         4 ONE        TWO2       THREE1
         5 ONE        TWO3       THREE1
         6 ONE        TWO3       THREE2

以下是我最初的解决方案:

SQL> SELECT seq,
  2         MAX(L1) over(PARTITION BY grp1) L1,
  3         MAX(L2) over(PARTITION BY grp2) L2,
  4         MAX(L3) over(PARTITION BY grp3) L3
  5    FROM (SELECT seq,
  6                 L1, MAX(grp1) over(ORDER BY seq) grp1,
  7                 L2, MAX(grp2) over(ORDER BY seq) grp2,
  8                 L3, MAX(grp3) over(ORDER BY seq) grp3
  9             FROM (SELECT seq,
 10                          CASE WHEN lvl = 1 THEN descr END L1,
 11                          CASE WHEN lvl = 1 AND descr IS NOT NULL THEN ROWNUM END grp1,
 12                          CASE WHEN lvl = 2 THEN descr END L2,
 13                          CASE WHEN lvl = 2 AND descr IS NOT NULL THEN ROWNUM END grp2,
 14                          CASE WHEN lvl = 3 THEN descr END L3,
 15                          CASE WHEN lvl = 3 AND descr IS NOT NULL THEN ROWNUM END grp3
 16                     FROM test))
 17   ORDER BY seq;

       SEQ L1         L2         L3
---------- ---------- ---------- ----------
         1 ONE                   
         2 ONE        TWO1       
         3 ONE        TWO2       
         4 ONE        TWO2       THREE1
         5 ONE        TWO3       THREE1
         6 ONE        TWO3       THREE2