LIMIT Yourself to MySQL No More

Using standard keywords: KEY vs. INDEX

CREATE TABLE `#__categories` (
  `id` int(11) NOT NULL auto_increment,
  -- ...
  PRIMARY KEY  (`id`),
  KEY `cat_idx` (`section`,`published`,`access`),
  KEY `idx_section` (`section`),
  KEY `idx_access` (`access`),
  KEY `idx_checkout` (`checked_out`)
) TYPE=MyISAM;

KEY here is not standard SQL -- this is actually a MySQL shortcut for creating indexes on columns within the table. The CREATE INDEX statement is a much more portable syntax across databases (including MySQL).

CREATE TABLE #__categories (
  id int(11) NOT NULL auto_increment,
  -- ...
  PRIMARY KEY  (id);
CREATE INDEX cat_idx ON #__categories (section, published, access);
CREATE INDEX idx_section ON #__categories (section);
CREATE INDEX idx_access ON #__categories (access);
CREATE INDEX idx_checkout ON #__categories (checked_out);