Question

I have a database. id – is a primary key.

id color
1 green
2 red
3 pink
4 pink
5 red

How do I remove repeated colors in SQL? The result will be:

id color
1 green
2 red
3 pink

Answer 1

In order to remove duplicates from your table, try a statement like this:

DELETE FROM my_table 
WHERE EXISTS (
  SELECT 1 FROM my_table t2
  WHERE my_table.color = t2.color
  AND my_table.id > t2.id
)

In English: Delete all records from my_table where there is another record in my_table with the same colour but with a lower ID. This will keep the record with the lowest ID per duplicate colour.

I suggest that after removing duplicates, you should add a unique constraint as indicated by LolCoder here