I have (all InnoDB) a parent table tbl1 with primary key some_id and child (referencing) table tbl2 with another_id referencing tbl1.some_id as foreign key. tbl2.another_id is not the primary key of tbl2 as this is a one to many relationship. Should my child table also have a primary key - maybe for indexing purposes?
The thread here almost answered my question but raised more questions about composite keys so I posted another question about that elsewhere...
Yes, you need to have a primary key on tbl2. This will allow you to uniquely identify each row which will be useful for many purposes in the future. You can read up on the importance of keys with a google search.