sql - 如何将 sql 结果条目旋转到列中(透视)

Question

我有表a

| id | value   | comment   |
|--------------------------|
|  1 | Some1   | comm1     |
|--------------------------|
|  2 | Some2   | comm2     |
|--------------------------|

我有表b，表a作为外键

| id | id_a  |name    | amount    | factor   |
|--------------------------------------------|
|  1 |  1    |Car     | 12        | 2        |
|--------------------------------------------|
|  2 |  1    |Bike    | 22        | 5        |
|--------------------------------------------|
|  3 |  2    |Car     | 54        | 1        |
|--------------------------------------------|
|  4 |  2    |Bike    | 55        | 4        |
|--------------------------------------------|

结果我想要一个组合:

|id| value | comment | Car_Amount | Car_factor | Bike_Amount | Bike_Factor |
|--------------------------------------------------------------------------|
| 1| Some1 | comm1   | 12         | 2          | 22          | 5           |
|--------------------------------------------------------------------------|
| 2| Some2 | comm2   | 54         | 1          | 55          | 4           |
|--------------------------------------------------------------------------|

据我所知，这不是一个支点。但我不确定这是否是个好习惯。我不是 SQL 方面的专家，但像这样混合表看起来完全错误。我的意思是“他们”希望将其作为一个平面结果用于报告...

有可能吗？

谢谢

Answer 1

像这样聚合值:

select 
      a.id, a.value, a.comment,
      sum(case when b.name='Car'  then b.amount end) as Car_Amount,
      sum(case when b.name='Car'  then b.factor end) as Car_Factor,
      sum(case when b.name='Bike' then b.amount end) as Bike_Amount,
      sum(case when b.name='Bike' then b.factor end) as Bike_Factor
from a left join b on a.id=b.id_a
group by  a.id, a.value, a.comment;