Question

I’m somewhat new to MySQL and I’m not sure how to do this or if it’s even possible.

I have a table like this:

Table products
    id  |  model  |  alt_model
    --     -----     ---------
    1      abc          abc
    2      ab-c         abc
    3      a-bc         abc
    4      def          def
    5      ghi          ghi
    6      gh-i         ghi
    7      jk-l         jkl
    8      mno          mno
    9      m-n-o        mno
    10     mn-o         mno
    11     m-no         mno
    12     pqr          pqr
    13     stu          stu

I want to be able to do a query that will result in every duplicate combination of products where the alt_models are the same. Each pair of duplicates is unique, switching their order should not yield another result, but the result should have the lower id in the id1 field

The result should look like this:

id1  |  id2   |  model1  |  model2
---     ---      ------     ------
 1       2       abc        ab-c
 1       3       abc        a-bc
 2       3       ab-c       a-bc
 5       6       ghi        gh-i
 8       9       mno        m-n-o
 8       10      mno        mn-o
 8       11      mno        m-no
 9       10      m-n-o      mn-o
 9       11      m-n-o      m-no
 10      11      mn-o       m-no

Is this possible?

Answer 1

A simple self join should do it;

SELECT a.id id1, b.id id2, a.model model1, b.model model2
FROM products a
JOIN products b
  ON a.alt_model=b.alt_model           -- alt_model must match
 AND a.id < b.id                       -- and id1 is smaller
ORDER BY id1,id2;

SQLfiddle for testing here.