Compare two rows in the same table for equality in SQL

Question

I have the following table in my database:

Table name: INSURANCE TABLE

ID | Policy 
1  | 34564  
2  | 67548  
3  | 34564  
4  | 98271  
5  | 90198  
6  | 98271  

I am looking for a sql query that will compare the Policy column values in all 5 rows and return those rows which have a value equal to atleast one other row.

For the table above I should get the following result set:

1 | 34564

3 | 34564
4 | 98271
6 | 98271

I would appreciate responses on how to write this query.

Answer 1

If I understand you, you want to group by Policy, discarding unique values:

select * from your_table where Policy in (
    select Policy from your_table group by Policy having count(*) > 1
);