[sqlite] Index question

[Taka Muraoka]

I have an object model that looks like this:

    OBJECT 1
    - item 1
    - item 2
    - item 3

    OBJECT 2
    - item 1
    - item 2

    OBJECT 3
    - etc...

These are stored in tables like this:

    CREATE TABLE object
    (
        object_id INTEGER PRIMARY KEY
    ) ;

    CREATE TABLE item
    (
        object_id INTEGER ,
        seq_no INTEGER
    ) ;

We retrieve items for a given object using this:

    SELECT * FROM item
    WHERE object_id = 12345
    ORDER BY seq_no ;
    
To speed up this up, I want to create an index on the item table. Am I
better off creating it on the object_id column alone or both object_id
and seq_no? What's the difference if I create a primary key on the item
table using object_id/seq_no?

Thanks.