Question

All the guys probably will recommend that I read the follow previously question in this URL http://senta.la/bd08

So I’m just read them carefully and I’m still with my problem. This situation its not equals of the question mentioned in link above.

See below the records I want to found (marked with *):

ID         COURSE       OTHERCOLUMN_X      OTHERCOLUMN_Y       OTHERCOLUMN_Z
123        2111         ...                ...                 ...
*5644      2245         ...                ...                 ...
*5644      2245         ...                ...                 ...
2121       2131         ...                ...                 ...

The previously programmer not thinking use the UNIQUE index to make a compost key to prevent this situation. I know… the good news is that programmer is not a programmer anymore.

This classic query its not provide the result I want…

SELECT id, course FROM mytable
GROUP BY id 
HAVING COUNT(id) > 1

I want to see only this results:

ID         COURSE       OTHERCOLUMN_X      OTHERCOLUMN_Y       OTHERCOLUMN_Z
*5644      2245         ...                ...                 ...
*5644      2245         ...                ...                 ...

I’m just tried a lot of queries but I can find one that show me the results above.

🙁

Answer 1

To find rows with duplicate id:

SELECT a.*
FROM mytable AS a
  JOIN
    ( SELECT id 
      FROM mytable
      GROUP BY id 
      HAVING COUNT(*) > 1
    ) AS b
    ON b.id = a.id

To find rows with duplicate (id, course):

SELECT a.*
FROM mytable AS a
  JOIN
    ( SELECT id, course 
      FROM mytable
      GROUP BY id, course 
      HAVING COUNT(*) > 1
    ) AS b
    ON  b.id = a.id
    AND b.course = a.course