title: Add new column to wordpress database
body: <p>I trying update my plugin. So I must upgrade mysql_table. But when trying new column, program get exception.</p>
  
  <p>This is my current table :</p>
  
  <pre><code>$sql = "CREATE TABLE  {$table_name} (
          say_id             int(11)   not null AUTO_INCREMENT,
          customer_mail      text      not null,
          customer_name  text      not null,
          customer_messagge      text      not null,
          messagge_date_time  datetime  not null,
  
          PRIMARY KEY (say_id)
          )ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=1";
  
          require_once(ABSPATH . "wp-admin/includes/upgrade.php");
          dbDelta($sql);
  </code></pre>
  
  <p>Now I am add colum more one table. I try Alter table, this working one time and add a column but one more refresh I get this error.</p>
  
  <p>This is mycode</p>
  
  <pre><code>$wpdb-&gt;query("ALTER TABLE wp_customer_say ADD say_state INT(1) NOT NULL DEFAULT 1");
  </code></pre>
  
  <p>And this is my error</p>
  
  <p>WordPress database error: [Duplicate column name 'say_state']
  ALTER TABLE wp_customer_say ADD say_state INT(1) NOT NULL DEFAULT 1</p>
  
  <p>I see this error and ı try this;</p>
  
  <pre><code>$query          = $wpdb-&gt;query("select * from wp_customer_say");
          $respond        = mysql_num_fields( $query );
          $column_array   = array();
  
          for($i = 0; $i &lt; $respond ; $i++):
              $column_array[]     = mysql_field_name($query,$i);
          endfor;
  
          if( !in_array("say_state",$column_array) ):
              $wpdb-&gt;query("ALTER TABLE wp_customer_say ADD say_state INT(1) NOT NULL DEFAULT 1");
          endif;
  </code></pre>
  
  <p>and I get this error.</p>
  
  <pre><code>Warning: mysql_num_fields() expects parameter 1 to be resource, integer given in
  </code></pre>
  
  <p>Help please. Thank you.
  Sorry bad english.</p>