How do I get data from another table in MySQL?

Question

I'm currently trying to link some databases up for a project I'm working on for my business. Here's my below SQL I'm using for my PHP website.

$sql = "SELECT lname, fname, designation, agency, mobile, direct, email FROM contacts";
$result = $conn->query($sql);

At the moment my output goes like this to show what's in each row using eg $lname=$lname["variable"]

       if ($result->num_rows > 0) {
          // output data of each row
          while($row = $result->fetch_assoc()) {
            
                  /* Print the row */ 
        echo "<tr>"."<td>". $lname . "</td><td>" . $fname . "</td><td>" . $designation . "</td><td>" . $agency . "</td><td>" . $mobile . "</td><td>" . $direct . "</td><td><a href='mailto:" . $email . "''>". $email. "</a><br>";
         }
}

I have another "clients" table, where each agency has an id - one that matches with $agency at this point. What I want to do is post the corresponding companyname column to that id.

How would I modify my code to do so (and access the column/rows from the secondary table)?

Answer 1

If I've understood the question correctly, the answer should look something like

SELECT ct.lname, ct.fname, ct.designation, ct.agency, ct.mobile, 
ct.direct, ct.email, cl.company_name 
FROM contacts ct 
JOIN clients cl ON ct.agency = cl.id

The crux of it is the SQL JOIN clause.