You don’t need to write your own queries, just use wordpress functions.
For instance, to get post by id; use get_post
<form method="POST">
<select name="post_ID">
<option value="21">21</option>
<option value="22">22</option>
</select>
<input type="submit" value="Get Selected Value" />
</form>
<?php
$post_id = $_POST['post_ID'];
if ( is_int( $post_id ) && !empty ($post_id ) ){
$post = get_post( $post_id );
if($post){
echo '<table>';
echo "<tr>";
echo "<th>Header 1</th>";
echo "<th>Header 2</th>";
echo "<th>Header 3</th>";
echo "<th>Header 4</th>";
echo "</tr>";
//foreach loop is removed because it will return only single object
echo '<tr><td>'.$post->post_title.'</td><td>'.$post->post_status.'</td><td>'.$post->post_date_gmt.'</td><td>'.$post->ID.'</td></tr>';
echo '</table>';
}
}
BTW, if you need to retrieve multiple posts then try get_posts