Filter out the duplicates based on a group in SQL

Question

I'm trying filter out the duplicates of the color column, but only for each group of parent_id , not the entire color column itself.

For example, I have the following table:

parent_id | child_id | color    |
5         | 1        | blue     |
5         | 2        | blue     |
5         | 3        | green    |
5         | 4        | green    |
5         | 5        | yellow   |
5         | 6        | orange   | 
6         | 7        | blue     |
6         | 8        | blue     |
6         | 9        | magenta  |
6         | 10       | green    |
6         | 11       | magenta  |
6         | 12       | orange   |

The result I am looking for is this:

parent_id | child_id | color    |
5         | 1        | blue     |
5         | 3        | green    |
5         | 5        | yellow   |
5         | 6        | orange   | 
6         | 7        | blue     |
6         | 9        | magenta  |
6         | 10       | green    |
6         | 12       | orange   |

Note how there is only one blue for parent_id = 5 , and one blue for parent_id = 6 . The same is true for the rest of the colors.

Any help on this is much appreciated.

Answer 1

select parent_id, min(child_id), color
from your_tab
group by parent_id, color;

Answer 2

If you want to delete them:

delete t
    from table t left join
         (select parent_id, color, min(child_id) as minci
          from table t
          group by parent_id, color
         ) pc
         on t.parent_id = pc.parent_id and t.color = pc.color and t.child_id = pc.minci
    where t.parent_id is null;