我想进行特定查询以将有关2个表的特定信息分组

Question

所以我有2个看起来像这样的表：

Factory
| name | timeoperating | operatedpieces |

Pieces
| serial | piecetype | unit (foreign key referencing factory.name) |

“ Pieces”中的“ Unit”是一个外键，引用了“ Factory”中的“ Name”。我想查询一个具有“名称”，“时间操作”，“操作件”的查询，然后再查询9列，每种类型（从P1到P9）有多少件连接了“单位”或“名称”的列。当然，每行一个名称。

我已经尝试了许多不同的方法，但是我从未得到过查询以返回与我想要的东西相似的东西，甚至有可能吗？

输出（第一行）：

| factory.name | factory.timeoperating | factory.operatedpieces |
  count(pieces.piecetype) where piecetype=P1 and unit=factory.name | 
  (then other 8 columns like the last one 
   but with piecetype = Px where X is the column number)

啊，我怕我自己不够清楚...

Answer 1

您可以使用9个“标量子查询”获得该数据。

例如：

select 
  f.name,
  f.timeoperating,
  f.operatedpieces,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 1) as c1,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 2) as c2,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 3) as c3,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 4) as c4,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 5) as c5,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 6) as c6,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 7) as c7,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 8) as c8,
  (select count(*) from pieces p where p.unit = f.name and p.piecetype = 9) as c9
from factory f