function is_clicker_already_returned($myclicker){ // Check if a clicker already returned
	global $wpdb;
	define ('FORM_NAME', 'Clickers Inventory');
	define ('FIELD_NAME', 'Clicker');
	$query="SELECT submit_time,
		if(field_name='".FIELD_NAME."', field_value, null ) AS '".FIELD_NAME."'
		FROM wp_cf7dbplugin_submits
		WHERE form_name = '".FORM_NAME."' AND field_value='".$myclicker."'";
	$myrows = $wpdb->get_results( $query, ARRAY_A );
	if (is_array($myrows) && count($myrows)){
		return true; //clicker already exists in the db
	}else{
		return false; // first time with this email
	}
}
function duplicate_clicker_validation_filter($result,$tag){
	define ('FIELD_NAME', 'Clicker');
	$type = $tag['type'];
	$name = $tag['name'];
	if($name == FIELD_NAME){ // Only apply to fields with the form field name of "clicker"
		$the_value = $_POST[$name];
		if(is_clicker_already_returned($the_value)){ //A clicker with this barcode has been returned)
			$result['valid'] = false;
			$result['reason'][$name] = 'clicker already returned.';
		}
	}
	return $result;
}
add_filter('wpcf7_validate_clicker','duplicate_clicker_validation_filter', 10, 2); // clicker field
add_filter('wpcf7_validate_clicker*', 'duplicate_clicker_validation_filter', 10, 2); // Req. clicker field