多列成行

Question

我需要什么查询来改变结果

来自

键值	属性1	价值1	属性2	价值2	属性3	价值3	属性4	价值4
12345	abc	54321	定义	是的	吉	没有	jkl	67890

**致**

键值	属性	价值
12345	属性1	值1
12345	属性2	值2
12345	属性3	值3
12345	属性4	值4

这是我对第一个表的查询

选择键值、属性1、值1、属性2、值2、属性3、值3、属性4、值4、属性5、值5 来自表A

我使用了 UNION ALL，但它显着减慢了进程，所以我不想使用 UNION ALL。

Answer 1

其他方式（ORACLE）：

select a.key_value
    , (
        case
            when b.rno = 1 then a.Attribute1
            when b.rno = 2 then a.Attribute2
            when b.rno = 3 then a.Attribute3
            when b.rno = 4 then a.Attribute4
        end
    ) as Attribute
    , (
        case
            when b.rno = 1 then a.Value1
            when b.rno = 2 then a.Value2
            when b.rno = 3 then a.Value3
            when b.rno = 4 then a.Value4
        end
    ) as Value
from (
    select '12345' as key_value, 'abc' as Attribute1,   '54321' as Value1, 'def' as Attribute2, 'Yes' as Value2, 'ghi' as Attribute3, 'No' as Value3, 'jkl' as Attribute4, '67890' as Value4 from dual
) a
cross join (
    select 1 as rno from dual
    union all
    select 2 as rno from dual
    union all
    select 3 as rno from dual
    union all
    select 4 as rno from dual
) b
;