Modify MySQL Query Based on Dropdown Menu

Question

I would like to be able to modify a MySQL query based on the selection in a dropdown menu. This would then update the subsequent table shown on the page.

The current code I have is below (note I'm using PHP code snippets (Insert PHP) plugin) however this doesn't have the desired result as no table is generated.

Any assistance would be greatly appreciated.

<form method="POST">
<select name="post_ID">
    <option value="21">21</option>
    <option value="22">22</option>
</select>
</form>

[insert_php]
global $wpdb;
echo $_POST['post_ID'];
$myQuery = $wpdb->get_results('SELECT * FROM ' . $wpdb->prefix.'posts' . 'WHERE ID = $_POST['post_ID']');

if($myQuery){
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 ( $myQuery as $result ) 
    {
        echo '<tr><td>'.$result->post_title.'</td><td>'.$result->post_status.'</td><td>'.$result->post_date_gmt.'</td><td>'.$result->ID.'</td></tr>';
    }
echo '</table>';
}
[/insert_php]

Answer 1

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