Question

数据：

+--------+------+------+------+------+
| WEEK_NO| Week1| Week2| Week3|Week4 |
+--------+------+------+------+------+
|      1 |  0.5 |  0.2 |  0.3 |0.4   |
|      2 |  0.5 |  0.2 |  0.3 |0.4   |
|      3 |  0.5 |  0.2 |  0.3 |0.4   |
|      4 |  0.5 |  0.2 |  0.3 |0.4   |
+--------+------+------+------+------+

期望的输出：

+--------+------+------+------+------+-------------+
| WEEK_NO| Week1| Week2| Week3|Week4 |COLUMN NEEDED|
+--------+------+------+------+------+-------------+
|      1 |  0.5 |  0.2 |  0.3 |0.4   |    0.5      |
|      2 |  0.5 |  0.2 |  0.3 |0.4   |    0.2      |
|      3 |  0.5 |  0.2 |  0.3 |0.4   |    0.3      |
|      4 |  0.5 |  0.2 |  0.3 |0.4   |    0.4      |
+--------+------+------+------+------+-------------+

Answer 1

使用CASE声明

SELECT CASE
         WHEN WEEK_NO = 1 THEN Week1
         WHEN WEEK_NO = 2 THEN Week2
         WHEN WEEK_NO = 3 THEN Week3
         WHEN WEEK_NO = 4 THEN Week4
       END AS "COLUMN NEEDED"
FROM   yourtable

或使用Decode

Select DECODE (WEEK_NO, 1, Week1, 
                        2, Week2, 
                        3, Week3, 
                        4, Week4) 
From yourtable

考虑更改表格结构

Answer 2

原始表格行中的数据重复是非常可疑的。显然我们对这个结构的目的一无所知，但它看起来似乎是数据建模的失败。应用First Normal Form会给...

create table weeks (
    week_no number primary key
    , week_coeff number not null )
/

所以查询将是：

select week_no
       , week_coeff as column_needed
from weeks
/

如果这看起来过于简单，请解释您正在建模的业务规则。

“但不知何故，数据出现在上述结构中，无法在源头进行更改。”

当然可以更改，它只是一个数据结构。但办公室政治是办公室政治。祝你好运，建立可怕的脆弱代码。

根据列中的值将多个列合并为一个列

2 个答案: