Question

I’m trying to make a query that will check for duplicates, and if I find duplicates I want to be able to update those accordingly. For example, I have the following data set, how do I only select the 2 rows that have the same value for ‘position’?

ID          position
1           0
2           1
3           2
4           1
5           3

In this example I would select rows 2 and 4 only.

Answer 1

SELECT t.position, 
    count(t.*) AS count 
FROM table t
GROUP BY position 
HAVING count(position) > 1

Should return an a list of positions and their repetition counts.

Edit: Neglected to alias my table

If you want to see the rows that have duplicate positions try:

SELECT t1.ID,
    t1.position,
    t2.ID,
    t2.position
FROM table t1
INNER JOIN table t2
    ON t1.ID < t2.ID
    AND t1.position = t2.position

This will give you a set of rows (4 columns) where there are duplicates. You will get 1 row for a duplicate, 3 for a triplicate, 6 for a quad, and it increases from that point on.