Question

basically i’d like to do:

SELECT * FROM `table` 
WHERE ( `col1`, `col2`) 
IN 
[
    SELECT `col1`, `col2` 
    FROM `table` 
    GROUP BY `col1`, `col2` 
    HAVING count(*) >1
]

i’d like this to select all unique duplicates and their actual duplicates.
but how can i keep the relationship between col1 and col2 relevant to the IN query?

i know there are other ways to do this.

one method is building a dummy table, moving all the relevant entries over to it, then replacing the original.

the other uses a join like:

SELECT * 
FROM table t1 
JOIN table t2 
ON t1.id > t2.id 
AND t1.col1 = t2.col1 
AND t1.col2 = t2.col2;

but that takes about 10 minutes to complete : \

Answer 1

This will show all duplicates, sorted together:

SELECT 
    t.* 
FROM 
        tableX  AS t
    JOIN 
        ( SELECT col1, col2 
          FROM tableX 
          GROUP BY col1, col2 
          HAVING COUNT(*) > 1
        )  AS td
      ON (td.col1, td.col2) = (t.col1, t.col2)
ORDER BY 
    t.col1, t.col2

An index on (col1, col2) would help the above – and also your Join version.