Assign domain values to the fields in MS SQL Server database
<p>I want to assign domain values to some columns in my <code>SQL Server</code> database to provide control to the data. How can I achieve that? I connected to the <code>SQL Server</code> database using <code>PHP PDO</code> and created the "Edit" option that allows the users to update the values. </p>

<p>How can I create dropdown options with a placeholder in that Edit file?   </p>

<pre><code>require_once('database.php');

if (isset($_POST['btn_submit'])) {
    $id = $_POST['txt_id'];
    $site = $_POST['txt_site_code'];

    if (!empty($site)) {

        try {
            $stmt = $conn-&gt;prepare("UPDATE FACILITY_TABLE_MILWAUKEE SET Site_Code=:site
                        WHERE OBJECTID = :id");

            $stmt-&gt;execute(array(':site' =&gt; $site, ':id' =&gt; $id));

            if ($stmt) {
                header('Location:index.php');
            }
        } catch (PDOException $e) {

        echo $e-&gt;getMessage();
    }
} 
else {
    echo "Input Site Code";
}
    $object_id = 0;
    $site = '';

 if (isset($_GET['id'])) {
    $id = $_GET['id'];
    $stmt = $conn-&gt;prepare("SELECT * FROM FACILITY_TABLE_MILWAUKEE WHERE OBJECTID=:id");
    $stmt-&gt;execute(array(':id' =&gt; $id));
    $row = $stmt-&gt;fetch();
    $object_id = $row['OBJECTID'];
    $site = $row['Site_Code'];
}

&lt;h2&gt;Edit the records&lt;/h2&gt;

&lt;form action="" method="post"&gt;
    &lt;table border="3px" cellpadding="5px"&gt;
        &lt;tr&gt;
            &lt;td&gt;Site Code&lt;/td&gt;
            &lt;td&gt;&lt;input type="text" name="txt_site_code"  value="&lt;?= $site; ?&gt;" readonly&gt;&lt;/td&gt;
        &lt;/tr&gt;

        &lt;tr&gt;
            &lt;td&gt;&lt;input type="hidden" name="txt_id" value="&lt;?= $object_id; ?&gt;"&gt;&lt;/td&gt;
            &lt;td&gt;&lt;input type="submit" name="btn_submit" value="Submit"&gt;&lt;/td&gt;
        &lt;/tr&gt;
    &lt;/table&gt;
&lt;/form&gt;
</code></pre>

<p>I have just included first two columns of the table. The table is huge. The last column of the table is "Action" where "Edit" option apperars.</p>