concatを使用してみてください:
$q = "SELECT * FROM `members` WHERE `first_name` LIKE :search_string
OR `last_name` LIKE :search_string
OR concat(`first_name` , ' ', `last_name`) LIKE :search_string";
concatを使用してみてください:
$q = "SELECT * FROM `members` WHERE `first_name` LIKE :search_string
OR `last_name` LIKE :search_string
OR concat(`first_name` , ' ', `last_name`) LIKE :search_string";