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while working on osCommerce-3 i got the table structure for category & categories_description as

CREATE TABLE IF NOT EXISTS `osc_categories` (
  `categories_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `categories_image` varchar(255) DEFAULT NULL,
  `parent_id` int(10) unsigned DEFAULT NULL,
  `sort_order` int(11) DEFAULT NULL,
  `date_added` datetime DEFAULT NULL,
  `last_modified` datetime DEFAULT NULL,
  PRIMARY KEY (`categories_id`),
  KEY `idx_categories_parent_id` (`parent_id`)

CREATE TABLE IF NOT EXISTS `osc_categories_description` (
  `categories_id` int(10) unsigned NOT NULL,
  `language_id` int(10) unsigned NOT NULL,
  `categories_name` varchar(255) NOT NULL,
  PRIMARY KEY (`categories_id`,`language_id`),
  KEY `idx_categories_desc_categories_id` (`categories_id`),
  KEY `idx_categories_desc_language_id` (`language_id`),
  KEY `idx_categories_desc_categories_name` (`categories_name`)

here i am not getting the meanning of indexing




What is the use of this indexing.What does it mean?



  1. These three indices are created for the tables specified in the brackets (categories_id, language_id, categories_name). The KEY keyword is a synonym for the INDEX keyword. It is no special magic behind it.

    I guess these three indexes are used to speed up data retrival/sorting operations on these tables.

    The index “idx_categories_desc_categories_id” is by the way redundant, “categories_id” already covered by left part of the composite index on the primary key.

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  2. The three tokens you mentioned


    are just names – there’s nothing special about them. They could have been called “foo”, “bar” and “baz” and that would have been just fine.

    They keep to the osCommerce naming convention of using idx_ for indexes, then the name of the table then the key field. But that’s just a developer’s convention; it’s not required by the database.

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