Postgres：根据行值选择列

Question

我有2张桌子：

表A

 Section | measure_name   |
---------+----------------|
 A       |      col1      |
 B       |      col2      |
 C       |      col3      |

表B

 Facility | col1| col2| col3| 
----------+-----+-----+-----+
 NY       |  5  | 50  |  90 |

我想写一个查询，从measure_name中选择Table A中的Table B。

Answer 1

似乎您希望从表B中获取与每个measure_name对应的列的值

如果是，则使用UNNEST()将表B转换为行，然后将其与表A联接。

with c AS
( SELECT 
       unnest(array['col1', 'col2', 'col3']) AS colname,
       unnest(array[col1, col2, col3]) AS value
FROM B
) 
SELECT a.*,c.value FROM A 
JOIN C ON a.measure_name = c.colname;

这给你

Section measure_name value
A       col1          5
B       col2         50
C       col3         90

Demo