sql - 将行转置为列并连接表

Question

嗨，我有两个表属性，实例

属性表

id  |    key_info   |   value_info
2   |     amount    |    1009
2   |   currency    |     USD
2   |     Level     |    Level 5
3   |    amount     |     2017 
3   |   currency    |     CAD

实例表

id   |  status
2    | Pending 
3    | Approved

我想像这样连接两个表-

新表

id | amount |  currrency | level   | status
2  |  1001  |     USD    | Level 5 | Pending
3  |   2017 |     CAD    |         | Approved

Attribute 和 Instance 中的所有字段都是可选的，除了 id。

Answer 1

select
  a.id,
  max(case when a.key_info = 'amount' then a.value_info end) as amount,
  max(case when a.key_info = 'currency' then a.value_info end) as currency,
  max(case when a.key_info = 'level' then a.value_info end) as level,
  i.status
from
  attribute a
  join instance i on a.id = i.id
group by
  a.id,
  i.status

Sql Fiddle