showSalesman.php

<?php
$servername = "localhost";
$username = "root";
$password = "mysql";
$dbname = "berkay_ersoy";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
} 

$sql = "SELECT salesman_name,count(product_id)
        FROM sale 
        INNER JOIN salesman sm
        USING (salesman_id)
        GROUP BY salesman_id;";
$result = mysqli_query($conn,$sql) or die("Error");

if (mysqli_num_rows($result) > 0) {
    // output data of each row
	echo "<table border='1'>";
    echo "<tr><td>SALESMAN NAME</td><td>ITEMS SOLD</td></tr>";
    while($row = mysqli_fetch_array($result)) {
		echo "<tr>";
        echo "<td>" . $row["salesman_name"]. "</td><td>" . $row["count(product_id)"]. "</td>";
		echo "</tr>";
    }
	echo "</table>";
} else {
    echo "0 results";
}
mysqli_close($conn);
?>