Question

SQL Table

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

Expected output (Return components of same price and manufactured yr as distinct combinations):

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

Query tried

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

Result from above query (wrong output though):

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

Please help me eliminating the duplicate combos using the query.

Answer 1

This works if no pairs of components share the same name:

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;

All I changed was to trade the inequality operator != for a greater than operator. This way you get every pair once instead of twice.

To provide for the possibility of identical names:

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

I assume id is unique, so it can’t go wrong.