建立PHP / MySQL联接查询的问题

Question

I am having some issues trying to construct this JOIN query. Any help is greatly appreciated! Thanks!

I have 3 tables here. Table A houses our "users." They are identified by the id number. Table C houses locations identified by an id number. Table B contains the connection between Table A and Table C. uid is the id of the user and lid is the id of the location. The user might be associated with multiple locations.

I need to build a query that will take the id of the user, find all of the locations that user's id is associated with and return them.

Table A

|     id     |     name     |
-----------------------------
|     0      |     steven   |
-----------------------------
|     1      |      etc     |
-----------------------------

Table B

|     id     |     uid      |     lid     |
-------------------------------------------
|     0      |      0       |      1      |
-------------------------------------------
|     1      |      1       |      1      |
-------------------------------------------

Table C

|     id     |   location_name   |
----------------------------------
|     0      |    santa monica   |
----------------------------------
|     1      |      hamptons     |
----------------------------------

Answer 1

You can Try like below

SELECT 
    A.id as user_id,
    A.name as user_name,
    C.location_name as location
FROM
    TableA A
        JOIN
    TableB B ON A.id = B.uid
        JOIN
    TableC C ON B.lid = C.id
WHERE
    A.id = 0;

Answer 2

SELECT u.id, u.name, l.id, l.location_name
FROM users u
JOIN connection c
ON c.uid = u.id
JOIN locations l
ON c.lid = l.id
WHERE u.id=?
GROUP BY l.id;  

Answer 3

   select A.name, C.location_name from B inner join A on B.uid=A.id inner join C on B.lid= C.id where A.id='".$id."' ;

$ id是您输入的用户名

Answer 4

I would say you remove that table B and have only table A and table C.

Table A

|     id     |     name     |
-----------------------------
|     0      |     steven   |
-----------------------------
|     1      |      etc     |
-----------------------------

Table C

|     id     |   location_name   |   uid  | 
-------------------------------------------
|     0      |    santa monica   |   0    |
-------------------------------------------   
|     1      |      hamptons     |   1    |
-------------------------------------------

The table C which I have proposed has a foreign key which references table A's id

Now you can have a query like,

select * from tableA A
inner join
tableB B on
A.id = B.uid