Question

I want to group items only when there are more than 2 rwos matching rule. How can this be done?

E.G: (grouping by Col)

Col 
----
A
A
B
B
B

Should return:

Col | count(*)
---------------
A     2
A     2
B     3

It only displays B once since there are more than 3 results.

Answer 1

Since MySQL doesn’t have COUNT OVER you need a inline view to get the counts for when the count is less then 3. Then its just a union to a normal count query

SELECT counts.col, 
       counts.k 
FROM   test 
       INNER JOIN (SELECT col, 
                          COUNT(col) k 
                   FROM   test 
                   GROUP  BY col
                   having count(col)  < 3 ) counts 
         ON test.col = counts.col 

UNION ALL 
SELECT col, 
       COUNT(col) k 
FROM   test 
GROUP  BY col 
HAVING COUNT(col) > 2 

See it working here