SQL JOIN遇到问题

Question

I'm having trouble with a MySQL JOIN and was wondering if someone could help me out. Real quick overview on the tables I'm joining.

User Table Columns (just the columns that matter in this case):

userId | active | role | username | addressId

Address Table Columns (just the columns that matter in this case):

addressId | firstName | lastName

ManagerRepRelationship table

repId | managerId

Here are the relationships between these tables:

• When a new User is created, they get assigned a key (userId) and their address information gets it's own row in Address with a key (addressId). That addressId key gets stores with the users row in the User table.

• Also, when a user is created they are assigned one of two roles: 'manager' or 'representative'. If they are a representative, they must be assigned a manager (so obviously, some managers need to be created before any reps can be). When a rep is assigned to a manager and created, the rep's userID is stored into the ManagerRepRelationship in the repId column, at the same time the manager's userId chosen for this rep is stored in the same row under the managerId column.

Here is the trouble I am having. When it comes to editing a representative, I want to echo the name of the manager that is assigned to that rep at the top. On the edit page, I am passing the edited representative's userId in the url so it is available with $_GET["userID'] .

I cannot seem to write the correct JOIN statement to get back the first and last name of the manager, not the rep being edited. Here is what I have so far but I am getting null. I hope I explained this well enough.

<?php
  $user_id = $_GET["userId"]; // the rep getting edited userId
  // grab all the reps address info and user info
  $user_result = mysqli_query( $connection,
                "SELECT Users.*, Address.*
                 FROM Users
                  JOIN Address
                  ON Users.addressId=Address.addressId
                 WHERE Users.userId=" . $user_id
              );
  $user_set = mysqli_fetch_array($user_result);

 // Trying to get the first and last name of the manager
 // That is assigned to this rep
   $result = mysqli_query( $connection,
                    "SELECT A.firstName, A.lastName
                     FROM Address A
                      JOIN Users U
                      ON A.addressId=U.addressId
                      JOIN ManagerRepRelationship M
                      ON M.repId=U.userId AND M.managerID=U.userId
                     WHERE U.role='manager' AND M.repId=" . $user_id
                   );
   $managerName = mysqli_fetch_array($result);
?>

Answer 1

This condition:

ON M.repId=U.userId AND M.managerID=U.userId

will only be true if a person is their own manager. I think what your looking for is something like this:

"SELECT
   A.firstName, A.lastName
FROM 
   Address A
   JOIN Users U ON A.addressId=U.addressId
   JOIN ManagerRepRelationship M ON M.managerID=U.userId
   WHERE U.role='manager' AND M.repId=" . $user_id

It should also be mentioned that your code is susceptible to SQL Injection and is therefore quite insecure.