Question

I have a few tables in a MySQL database similar to this setup:

major table

---------------------
| id | name         |
|-------------------|
|  0 | Architecture |
|  1 | Biology      |
|  2 | Chemistry    |
---------------------

college table

----------------------
| id | name          |
|--------------------|
|  0 | Georgia Tech  |
|  1 | Virginia Tech |
|  2 | Cal Tech      |
----------------------

users table

----------------------------------------------
| id | name          | major_id | college_id |
|--------------------------------------------|
|  0 | John Smith    |       2  |         0  |
|  1 | Kevin Lee     |       2  |         1  |
|  2 | Matt Anderson |       0  |         2  |
----------------------------------------------

Using PHP, I want to get all the information for a user using a query similar to this:

SELECT * FROM users WHERE name=`$user`

Is there someway for MySQL to automatically link the “major_id” and “college_id” columns to the “major” and “college” tables in a way where the query above would return the appropriate values?

If it is not possible with a single query, would multiple queries slow down performance considerably?

Answer 1

SELECT * FROM users WHERE name='$user'

This query (yours has back ticks around $user, back ticks are for column names, use double/single quotes) will only return values from the users table. You can’t make MySQL “automagically” construct your joins. You have to do it explicitly, otherwise, how would you get information only from the users table if you wanted to? Use a JOIN like this:

SELECT users.name AS Username, college.name AS College, major.name AS Major
FROM users
INNER JOIN college ON users.college_id = college.id
INNER JOIN major ON users.major_id = major.id 

Limit the retrieved columns by only selecting the ones you really need. So instead of the asterisk, write users.name etc.

The JOIN syntax is described in the MySQL Docs.