Postgresql：将列拆分为行

Question

我有一张这样的表：

gid | cat1 | cat2 | some_value
-------------------------------
 1  |  A   | 100  |    I 
 2  |  B   | 200  |    II
 3  |  C   | 300  |    III
 4  |  D   | 400  |    IV

我想将此表转换为类似的内容，即将列值转换为行值：

gid | category | value | some_value
-----------------------------------
 1  |   cat1   |   A   |     I
 1  |   cat2   |  100  |     I
 2  |   cat1   |   B   |     II
 2  |   cat2   |  200  |     II
... |   ...    |  ...  |     ...

这是否可以在Postgresql中使用？

Answer 1

使用Union：

Select gid, 'cat1' as category, cat1 as value, some_value from t
union all
Select gid, 'cat2' as category, cast(cat2 as varchar(100)) as value, some_value from t
order by gid

这是一个fiddle。