Join Users and Orders

Given two DataFrames of users and orders, return all user-order pairs that share a matching user_id, sorted by user_id then order_id.

Schema

users

column	type
user_id	int
name	str

orders

column	type
user_id	int
order_id	int
amount	float

Sample Input

users

user_id	name
1	Alice
2	Bob
3	Carol

orders

user_id	order_id	amount
1	101	50.0
1	102	80.0
2	103	30.0

Expected Output

user_id	name	order_id	amount
1	Alice	101	50.0
1	Alice	102	80.0
2	Bob	103	30.0

Explanation

Only users with at least one matching order are included; user 3 (Carol) has no orders so she is excluded.