Question

I have a fairly simple table called widgets. Each row holds an id, a description, and an is_visible flag:

CREATE TABLE `widgets` (
  `id` int auto_increment primary key, 
  `description` varchar(255), 
  `is_visible` tinyint(1) default 1
);

I’d like to issue a query that selects the descriptions of a subset of visible widgets. The following simple query does the trick (where n and m are integers):

  SELECT `description` 
    FROM `widgets` 
   WHERE (`is_visible`) 
ORDER BY `id` DESC 
   LIMIT n, m;

Unfortunately this query, as written, has to scan at least n+m rows. Is there a way to make this query scan fewer rows, either by reworking the query or modifying the schema?

Answer 1

Use indexes for faster query result:

ALTER TABLE `widgets` ADD INDEX ( `is_visible` )