Linking SQL Tables - Issue - php

Question

I would like to link two SQL tables together, both the tables have data entered in them through HTML/PHP forms.
The first table is where the user enters all their details into a form (called system), and the second table is for where a user fills out another form for booking (called users). How do I link these tables together? To show the users booking(s).
I don't know how to get the booking table/form to echo out the user's username into the second table to link them together?
I understand that this does not make sense but would really appreciate some help!!!
Here is the first table's SQL for creating a user account:
And, here is the SQL for creating a booking?:
</form>
</body>
</html>
<br></br>
</div>
</div>
</div>
</body>
</html>
Here is the code that links what the user entered for the booking form (system table) to the SQL database.

Answer 1

Two tables can be "linked" together using JOIN. If you want to list the bookings (rows in the details table), with some user information, you can use LEFT OUTER JOIN or INNER JOIN. (The difference is that with LEFT OUTER JOIN you get all the bookings even if some of them don't have a user. With INNER JOIN you get only the bookings where there exists a corresponding row in users.)
If a column has the same name in two different tables, you can use users.user_uid and details.user_uid to refer to them.
SELECT details.*, user.email, user.first, user.last
FROM details LEFT OUTER JOIN user ON user.user_id = details.user_uid;
Then you maybe want to add a WHERE or ORDER BY and perhaps a LIMIT.
In the users table, there is a user_id (INT) and a user_uid (VARCHAR). The details table has a user_uid (INT). In the example, I was assuming that the user_uid in the details table corresponds to the user_id in the users table because these are both INT. You might want to change the name of some column to make it less confusing. Let's assume you want to rename users.user_uid to "username".
Also, you should add a unique index on the user_id and username, assuming that you want both of them to be unique. For the INT, I suggest you make this the primary key with automatically incrementing numbers and the username, just a unique key:
CREATE TABLE users (
user_id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
... ,
username VARCHAR(20) NOT NULL UNIQUE,
...
);
In the details table you probably also want to make the ID a PRIMARY KEY with AUTO_INCREMENT.
A unique key guarantees that there are no duplicates and it also makes lookups on these columns efficient.

Answer 2

If you are just trying to query them together a join should do the trick.
SELECT users.user_first, users.user_last, users.user_email, system.* FROM system INNER users JOIN ON users.user_uid = system.user_uid
In order to store the user_uid value in the system table you need to add a hidden input in your form like this:
<input type="hidden" name="uid" value="<?php echo $_SESSION['u_id']; ?>">
then in your php add
$user_uid = $_POST['uid'];
and insert it when you run your insert query.
INSERT INTO system (date, time, table_layout, user_uid) VALUES ('$date', '$time', '$table_layout', '$user_uid');
Just make sure that your table actually has that column. Once that value is available you should be able to run the above join query.

Answer 3

Let's see. You have two tables, one with user data (users), and one with booking data (details). A "details" row contains an ID of the user linked to that particular row.
Once you know, at least, the ID of the booking, you can get the id of the user like this:
SELECT user_uid FROM details WHERE ID = #specificBookingID
Once you know the user id you can get the user data:
SELECT * FROM users where user_uid = #retrievedUserID
You can do it in one query like so:
SELECT * FROM users where user_uid IN (SELECT user_uid FROM details WHERE ID = #specificBookingID)