How can I find duplicate entries and delete the oldest ones in SQL?

Question

I've got a table that has rows that are unique except for one value in one column (let's call it 'Name'). Another column is 'Date' which is the date it was added to the database.

What I want to do is find the duplicate values in 'Name', and then delete the ones with the oldest dates in 'Date', leaving the most recent one.

Seems like a relatively easy query, but I know very little about SQL apart from simple queries.

Any ideas?

Answer 1

Find duplicates and delete oldest one

Here is the Code

create table #Product (
    ID      int identity(1, 1) primary key,
    Name        varchar(800),
    DateAdded   datetime default getdate()
)

insert  #Product(Name) select 'Chocolate'
insert  #Product(Name,DateAdded) select 'Candy', GETDATE() + 1
insert  #Product(Name,DateAdded) select 'Chocolate', GETDATE() + 5
select * from #Product

;with Ranked as (
    select  ID, 
        dense_rank() 
        over (partition by Name order by DateAdded desc) as DupeCount
    from    #Product P
)
delete  R
from    Ranked R
where   R.DupeCount > 1

select * from #Product

Answer 2

delete from table a1 where exists (select * from table a2 where a2.name = a1.name and a2.date > a1.date)