SQL INSERT with LEFT JOIN :     $sql3="INSERT INTO users_addresses (ua_user_id,ua_address_id) LEFT JOIN users ON users_addresses.ua_user_id=users.user_id LEFT JOIN addresses ON users_addresses.ua_address_id=addresses.address_id"

I want when the forms are completed to fill the users_addresses with the id of the user and the id from the address tables.But for now the sql doesn't fill nothing in the table users_addresses[These are my tables][1]


  [1]: https://i.stack.imgur.com/Qg9B4.jpg