Question

我有一个有两列的Oracle DB表。我希望看到每一行重复的次数与第二列中存储的次数相同。该表如下所示：

col1 col2  
a    2  
b    3  
c    1

我想编写一个返回此内容的查询：

因此col2的值决定了行重复的次数。有没有一种简单的方法来实现这一目标？

谢谢！

Answer 1

SQL Fiddle

Oracle 11g R2架构设置：

CREATE TABLE test ( col1, col2 ) AS
          SELECT 'a', 2 FROM DUAL
UNION ALL SELECT 'b', 3 FROM DUAL
UNION ALL SELECT 'c', 1 FROM DUAL

查询1 ：

SELECT col1,
       col2
FROM   test t,
       TABLE(
         CAST( 
           MULTISET(
             SELECT LEVEL
             FROM   DUAL
             CONNECT BY LEVEL <= t.col2
           )
           AS SYS.ODCINUMBERLIST
         )
       )

<强> Results ：

| COL1 | COL2 |
|------|------|
|    a |    2 |
|    a |    2 |
|    b |    3 |
|    b |    3 |
|    b |    3 |
|    c |    1 |

Answer 2

with src (col1, col2) as (
    SELECT 'a', 2 FROM DUAL UNION ALL
    SELECT 'b', 3 FROM DUAL UNION ALL
    SELECT 'c', 1 FROM DUAL
)
SELECT
    src.*
FROM
    src
    JOIN (
        SELECT LEVEL val FROM DUAL
        CONNECT BY LEVEL <= (SELECT MAX(col2) FROM src)
    ) gen ON gen.val <= src.COL2
ORDER BY
    src.col1

或在Oracle 12中可以使用

with src (col1, col2) as (
    SELECT 'a', 2 FROM DUAL UNION ALL
    SELECT 'b', 3 FROM DUAL UNION ALL
    SELECT 'c', 1 FROM DUAL
)
SELECT
    src.*
FROM
    src
    CROSS APPLY (SELECT NULL FROM DUAL CONNECT BY LEVEL <= src.col2)
ORDER BY
    col1;

Answer 3

这是另一种选择（我添加了一个额外的列只是为了显示其他列可以存在），假设col1是唯一的：

with src (col1, col2, col3) as (
    SELECT 'a', 'b', 2 FROM DUAL UNION ALL
    SELECT 'b', 'c', 3 FROM DUAL UNION ALL
    SELECT 'c', 'd', 1 FROM DUAL
)
select col1, col2, col3
from   src
connect by level <= col3
           and prior col1 = col1
           and prior sys_guid() is not null;

COL1 COL2       COL3
---- ---- ----------
a    b             2
a    b             2
b    c             3
b    c             3
b    c             3
c    d             1

Answer 4

如果a是你的桌子，那么你也可以这样做：

select a1.col1 , a1.col2 
      from a a1
      join  (select level col2  from dual 
      connect by level < ( select max(col2) + 1 from a))   a2
      on a2.col2 between 1 and a1.col2

如何根据列的值展开Oracle查询的结果

4 个答案: