MS Access 查找重复项

Question

I have a MS Access table that had duplicate entries loaded to it. I used the query wizard and it returns both records. I need to return one record preferably with the id so I can use it to delete only the duplicate. Its been awhile since I used MS Access can this be done?

 UpdateTable
   ID
   PkgId
   CompName
   UpdDate   
   UpdQty

Data:

7212797   ADJ  E5780   9/27/2019 7;  
7213166   ADJ  E5780   9/27/2019 7; 
7212708   ADJ  E5912   9/27/2019 7;
7213167   ADJ  E5912   9/27/2019 7;

Answer 1

Consider the approach using a correlated subquery with an EXISTS condition:

SELECT id
FROM mytable t
WHERE EXISTS (
    SELECT 1 
    FROM mytable t1
    WHERE 
        t1.PkgId = t.PkgId 
        AND t1.CompName = t.CompName
        AND t1.UpdDate = t.UpdDate
        AND t1.UpdQty = t.UpdQty
        AND t1.id < t.id
)

This will return all id for which a duplicate exists (ie same pkgId/CompName/UpdDate/UpdQty ). The record with the lowest id is considered the original record and will not be returned by the query.

Answer 2

If you want to delete the records, there are multiple ways. I would go for a comparison on the id column:

delete from t
    where t.id < (select max(t2.id)
                  from t as t2
                  where t2.compname = t.compname and
                        t2.upddate = t.update and
                        t2.updqty = t.updqty and
                 );

That said, this will not work if any of the comparison columns are null . If id is a primary key, you can instead use:

delete from t
    where t.id not in (select max(t2.id)
                       from t t2
                       group by pkgid, compname, upddate
                      );