T-SQL Logic (Where exists one column but not the other)

I need a bit of logical help in writing a query.

Here is the set up.

create table main_table 
(
    id varchar(10) not null,
    seq varchar(10) not null
)

insert into main_table (id, seq) 
values ('A1', '1'), ('A1', '2'),
       ('A1', '3'), ('A2', '1'),
       ('A2', '2'), ('A2', '3'),
       ('A3', '1'), ('A3', '2'),
       ('A3', '3');
go

create table sub_table 
(
    id varchar(10) not null,
    seq varchar(10) not null
)

insert into sub_table (id, seq) 
values ('A1', '1'), ('A1', '2'), ('A2', '1');

I need a query that returns all records from main_table where the id of main_table matches the id of sub_table, but seq of main_table does not match seq of sub_table.

Expected result is

id	seq
A1	3
A2	2
A2	3

My attempt

select
    a.id, a.seq 
from 
    main_table a
where 
    exists (select 1 from sub_table b
            where a.id = b.id and a.seq != b.seq)

What is the right query to do this?

Answer

Here’s one way (Fiddle)

SELECT a.id,
       a.seq
FROM   main_table a
       JOIN sub_table b
         ON a.id = b.id
GROUP  BY a.id,
          a.seq
HAVING MAX(CASE WHEN a.seq = b.seq THEN 1 ELSE 0 END) = 0 

Or

SELECT a.id,
       a.seq
FROM   main_table a
WHERE  a.id IN (SELECT b.id
                FROM   sub_table b)
       AND NOT EXISTS (SELECT 1
                       FROM   sub_table b
                       WHERE  a.id = b.id
                              AND a.seq = b.seq)