Select equal values from column with inner join (sql) - mysql

Question

I am pretty new to SQL, so please dont go too hard on me :(
I have got two tables - "cart" and "orders". In the "cart" table are all the things a random user has ordered - in this case these few rows (with the column names above):
session_id - product_id - product - product_name - price - quantity
1 - 1 - Table - Something - 10.00 - 1
1 - 2 - Chair - SomethingNew - 20.00 - 1
2 - 2 - Chair - SomethingNew - 20.00 - 1
I want to write a statement that selects all the orders with the same session_id - in this case the number 1 - and copy it into the "orders" table, because all the items with the same session id should be labeled as one big order - but i don't want to hard code it (with select and session_id=1 for instance)...
This is what i have got so far for my selection:
I tried using a inner/self join, so that i can check if the values are the same
SELECT * from cart JOIN cart AS cartB
WHERE cart.session_id = cartB.session_id
GROUP BY cart.session_id;
But this currently gives me the following rows as solution:
session_id - product_id - product - product_name - price - quantity
1 - 1 - Table - Something - 10.00 - 1
2 - 2 - Chair - SomethingNew - 20.00 - 1
Instead of (what i would have wanted):
session_id - product_id - product - product_name - price - quantity
1 - 1 - Table - Something - 10.00 - 1
1 - 2 - Chair - SomethingNew - 20.00 - 1
EDIT: I know, the 2nd and 3rd rows are pretty similar. But thats exactly why the session id is very important in this case, and why i'd like to make it work.
What am i doing wrong? Is the inner join even needed? I am really having some problems with the statment since i am a huge beginner here.. but my code would make sense to me.. :(
Big thanks to everybody who takes his time to read this (and maybe even help)!

Answer 1

At the moment I see here 2 options:
Either your PROGRAM passes to SQL the session IDs for orders that you want to copy to orders table, -- which would be normal in any webshop.
In which case you have to get the correct session_id= from your program and pass it to your SQL query as a parameter, eg. in PHP.
Or you want to copy ALL session_id'd cart contents into orders. In which case it is even simpler, without any WHERE: INSERT INTO order SELECT * FROM cart;
If you want something else, you should specify, how it is determined WHICH session_id's need to be copied from cart to orders.
UPD. And you are right, the JOIN in your example doesn't appear to do anything useful.