SQL选择具有（部分）重复数据的行

Question

我有以下数据库架构：

Product ID | Component | ...

产品ID - 外键

组件 - 产品的一部分

出于某些奥术原因，许多唱片都拥有相同的产品ID＆amp;零件。是否有SQL查询将返回所有产品ID＆amp;组件有多个相同的组件？

E.g。给出下表

| Product ID | Component |
--------------------------
| 1          | c1000     |
| 1          | c1100     |
| 2          | c2000     |
| 2          | c2000     |
| 2          | c2200     |
| 3          | c3000     |

SQL查询应返回：

| Product ID | Component |
--------------------------
| 2          | c2000     |

Answer 1

SELECT ProductId, Component, count(*) Duplicates
 from MyTable  --  or whatever
 group by ProductId, Component
 having count(*) > 1

这也会显示有多少重复条目。

Answer 2

SELECT
  ProductId,
  Component
FROM
  Table
GROUP BY
  ProductId,
  Component
HAVING
  COUNT(*) > 1

Answer 3

select "Product ID", Component
from table
group by "Product ID", Component
having count(*) > 1