从以下SQL查询中删除重复项

Question

SQL表

id       component   price  manufactured
1         fx card   500     2011
2         ram       400     2010
3         case      400     2010
4         smps      500     2011
5         cord      200     2010
6         usb       200     2010

预期产出（返回相同价格的组件，并按不同的组合制造）：

component   component   price   manufactured
smps        fx card     500     2011
case        ram         400     2010
cord        usb         200     2010

查询已尝试

SELECT m1.[component]
  ,m2.[component]
  ,m1.[price]
  ,m1.[manufactured]
FROM [dbo].[Mfg] m1
inner join [dbo].[Mfg] m2
on m1.component != m2.component 
and m1.price = m2.price 
and m1.manufactured = m2.manufactured

来自上述查询的结果（但输出错误）：

component   component   price   manufactured
smps        fx card     500    2011
case        ram         400    2010
cord        usb         200    2010
ram         case        400    2010
fx card     smps        500    2011
usb         cord        200    2010

请帮我删除使用查询的重复组合。

Answer 1

如果没有任何组件对共享相同名称，则此方法有效：

SELECT m1.[component]
      ,m2.[component]
      ,m1.[price]
      ,m1.[manufactured]
FROM [dbo].[Mfg] m1
JOIN [dbo].[Mfg] m2 ON m1.component > m2.component 
                   AND m1.price = m2.price 
                   AND m1.manufactured = m2.manufactured;

我改变的只是为!=运算符交换不等运算符greater than。这样你就可以得到每一对而不是两次。

提供相同名称的可能性：

JOIN [dbo].[Mfg] m2 ON m1.id > m2.id
                   AND m1.price = m2.price 
                   AND m1.manufactured = m2.manufactured;

我认为id是唯一的，所以它不会出错。