Insert into multiple tables from one form (mysql and PHP) - php

Question

I'm new to this site and coding so please go easy on me if you come across some rookie mistakes.
I have a single form that when submitted it inserts data into two separate tables (users, users_addresses). The user address should be linked back to the user by the User's ID.
I have seen a couple different methods that can be used for this type of problem (and none which IC an get to work), but I'm reaching out for help to see which would be the best way.
This is what I have so far:
public function createNewUser($details, $active)
{
$password = $details["password"];
$username = strtolower($details["username" ]);
$firstname = strtolower($details["firstname"]);
$lastname = strtolower($details["lastname" ]);
$email = strtolower($details["email" ]);
$sex = strtolower($details["sex" ]);
$datepicker = strtolower($details["datepicker" ]);
$disabled = ($active) ? "0" : "1";
$address1 = strtolower($details["address1" ]);
$address2 = strtolower($details["address2" ]);
$province = strtolower($details["province" ]);
$city = strtolower($details["city" ]);
$district = strtolower($details["district" ]);
$zipcode = strtolower($details["zipcode" ]);
$
$sql = "INSERT INTO users VALUES (NULL, LOWER('$username'), MD5('$password'), LOWER('$firstname'), LOWER('$lastname'), LOWER('$email'), LOWER('$sex'), LOWER('$datepicker'), 0, NOW(), $disabled, 0)";
$resultSet = $this->db->query($sql);
return $this->db->getInsertId();
$sql = "INSERT INTO users_addresses VALUES (NULL, LOWER('$userid'), LOWER('$address1'), LOWER('$address2'), LOWER('$province'), LOWER('$city'), LOWER('$district), LOWER('$zipcode')";
$resultSet = $this->db->query($sql);
return $this->db->getInsertId();
}

Answer 1

The second query is never executed as you have a return statement before it executing in all conditions. Even if that is corrected, $user_id in second query has not been filled with value obtained from first query. Solution is below:
First
return $this->db->getInsertId();
should be replaced by
$user_id=$this->db->getInsertId();
Second
return $this->db->getInsertId();
should be replaced by
return $user_id

Answer 2

There is quite something wrong / strange with your code:
Don't put variables directly in SQL code, use prepared statements instead.
You are calling strtolower and LOWER on all the data. No need to do it twice.
The second query is never done, because you return before it. That's "unreachable code".
The fix is probably done by replacing the first return $this->db->getInsertId() with $userid = $this->db->getInsertId() and the second one with return $userid.
Good luck and welcome to SO.