SQL - find the duplicates

Question

select * from table1 where destination in  ('chi','usa','ind')

Ideally my result set should be 3 rows. one row for each destination.

But in my result there are duplicates.

chi
usa
ind
usa

I want to find which destination is duplicated. I have hundreds of destination and i want to delete the duplicate records. I am not looking for distinct. Am looking for the duplicated ones.

Answer 1

Use group by and having instead of distinct

select destination from table1 
where destination in  ('chi','usa','ind')
group by destination 
having count(*)>1

If you want to delete these and retain one, it gets a little messy. This is probably the shortest way, but its a bit of a hack.

delete from destination where id not in (
    select max(id) from table1
      where destination in  ('chi','usa','ind')
      group by destination 
    ) 

Answer 2

This will give you a count of duplicates, ordered by number of dupes desc:

SELECT CountryAbbr,
       COUNT(*) AS DuplicateCount
FROM   YourTable
GROUP BY CountryAbbr
HAVING COUNT(*) > 1
Order By 2 DESC

Answer 3

Add group by at the end... should give you two columns, on is the country, the other is how many times it was in the list.

So..

select * from table1 where destination in  ('chi','usa','ind') group by destination

Hope this helps