Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE Order_items ( order_id VARCHAR, product_id VARCHAR )

### Question ###
Show order ids and the number of products in each order.

### Accurate SQL ###

SELECT order_id, COUNT(DISTINCT product_id) FROM Order_items GROUP BY order_id