This is a SQL question, not perl

Anyway see : https://stackoverflow.com/questions/2594829/finding-duplicate-values-in-a-sql-table.

Your query will have to be something like:

SELECT
    y.id,y.name,y.email
    FROM @YourTable y
        INNER JOIN (SELECT
                        name,email, COUNT(*) AS CountOf
                        FROM @YourTable
                        GROUP BY name,email
                        HAVING COUNT(*)>1
                    ) dt ON y.name=dt.name AND y.email=dt.email
[download]

UPDATE: The following schema/query gets the desired result:

sqlite> 
CREATE TABLE "table"(ID,Tag1,Tag2);
-- Populate table, then"
select * from "table";
ID          Tag1        Tag2      
----------  ----------  ----------
1           science     math      
2           science     algebra   
3           history     math      
4           science     math      

sqlite>
   SELECT t.id,t.tag1,t.tag2  from "table" t 
        inner join ( SELECT  Tag1, Tag2, COUNT(*) c
                     FROM 'table' 
                     GROUP BY Tag1, Tag2 
                     HAVING c > 1) x
        on t.tag1=x.tag1  and t.tag2=x.tag2;
ID          Tag1        Tag2      
----------  ----------  ----------
1           science     math      
4           science     math
[download]