How to select datas that doesnt match in another column

Question

So i have this table A:

color        ID       MODEL
-----------------------------
red        | 10   |   HONDA
blue       | 10   |   TOYOTA
red        | 15   |            


        

Answer 1

Use NOT EXISTS to find rows with matching id but different colors:

select *
from yourtable a
where a.color IN ('red', 'blue')
  and not exists (
    select 1
    from yourtable b
    where a.id = b.id
      and b.color NOT IN ('red', 'blue')
    )

Notes:

• for efficient lookup consider adding indexes ( more distinct values means higher efficiency of tree traversal )
• consider normalizing your data with additional dictionary color table