how to link a customer and a project to oneanother? - php

Question

I'm kind of new to PHP/MySQl so I would like some guidelines on how these thing work, hard to google this...
So, im trying to learn php/mysql and I'm about to write a small page with customers and each customer could have a few projects.
so, my db is set up as follows (guess this would need heavy modifications):
- customers (id, name, description)
- projects (id, name, description)
- users (id, name )
<?php
if(isset($_GET['id'])) {
$query = "SELECT * FROM customers WHERE id = '". $_GET['id']."'";
$results = mysql_query($query);
while($row = mysql_fetch_array( $results ))
{
echo "<h3>" . $row['name'] . "</h3>";
echo "<br />";
$query = "SELECT * FROM projects ORDER by name ASC";
$results = mysql_query($query);
echo "<table>
<tbody>";
while($row = mysql_fetch_array( $results ))
{
echo "<tr>
<td><a href='main.php?id=" . $row['id'] . "'>" . $row['name'] . "</a></td>
<td>" . $row['description'] . "</td>
</tr>";
}
echo "</tbody>
</table>";
}
} else {
$query = "SELECT * FROM customers ORDER by name ASC";
$results = mysql_query($query);
echo "<table>
<thead>
<tr>
<th width='20%'>Customer</th>
<th width='80%'>Description</th>
</tr>
</thead>
<tbody>";
while($row = mysql_fetch_array( $results ))
{
echo "<tr>
<td><a href='main.php?id=" . $row['id'] . "'>" . $row['name'] . "</a></td>
<td>" . $row['description'] . "</td>
</tr>";
}
echo "</tbody>
</table>";
}
?>
As you can see it missing some heavy things, for instance, if I choose Customer A or B I receive the same projects, I don't know how to separate the projects and "bind" them to a certain customer. And my intention is to "bind" users to projects and customers as well.
Any hints into the correct direction is appreciated!

Answer 1

You can have an INNER JOIN in the select query, like so:
"SELECT * FROM customers c INNER JOIN projects p ON p.name = c.name WHERE c.id = '". $_GET['id']."'";
Here, I have considered that you DO HAVE a name column in customer table which is the same as that in project.

Answer 2

You would need to add some tables.
First a table that represents the relation from Customers to Projects. This would be like
Customer ID | Project ID
1 | 1
2 | 3
....
Same would be needed for Customer and User.
Now you can reference to this table to get your needed information and perform the necessary joins to get your data.

Answer 3

You need another table which has the key (customers.id,projects.id) In this way you link each customer to their own projects, and you'd need to select the data from that table depending on the id of the customer. Probably you'll need a customer/user table too, to link user id to customer id.
Edit for clarity: The new table should look something like:
CREATE TABLE customer_projects (
customer_id INT NOT NULL,
project_id INT NOT NULL,
PRIMARY KEY (customer_id, project_id));
Then you assign each customer to their projects in this table. To get the details (customer name, project name), you'd need to do a "join" with other tables, something like:
SELECT customers.*, projects.* FROM customer_projects
LEFT JOIN customers ON customers.id = customer_projects.customer_id
LEFT JOIN projects ON projects.id = customer_projects.project_id
WHERE customer_projects.customer_id = '1' // 1 is an example of a customer id.