MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

create table cart_items(id int, cart_id int, sku int, qty int)
insert into cart_items values(64903,4935153,15628,1),
(65108,4935153,34929,4),
(65109,4935153,35870,4)
create table shipping_table(id int, invoice int, sku int, qty int, order_id int)
insert into shipping_table values(99,104,15628,1,9313),
(98,104,34929,2,9313),
(97,103,34929,1,9313)
SELECT 
     CT.sku, 
     qty as total_qty, 
    (select SUM(qty) from shipping_table MT where CT.sku=MT.sku group by MT.sku) 
    as total_shipped_qty 
FROM cart_items CT
      WHERE CT.cart_id = '4935153' 


sku
total_qty
total_shipped_qty


15628
1
1

34929
4
3

35870
4
null