Indexes are data structures that improve retrieval speed for data in a database. They work by sorting field values and storing pointers to records, allowing for faster searching. Indexes should be used on fields involved in searches, joins, or with high cardinality. There are different types of indexes including clustered, non-clustered, unique, non-unique, bitmap and full text. Indexes are created using SQL commands and their information can be displayed and deleted as needed.

1. INDEXING Davood Pour Yousefian Barfeh

13. When should indexing be used? SELECT n.newstitle, c.categoryname FROM categories c, newsitem_categories nc, newsitem n WHERE c.categoryid=nc.categoryid AND nc.newsid=n.newsid; These fields must be indexed: newsitem  newsid newsitem_categories  newsid newsitem_categories  categoryid categories  categoryid CREATE INDEX newscat_news ON newsitem_categories(newsid); CREATE INDEX newscat_cats ON newsitem_categories(categoryid); Ex. CREATE TABLE newsitem ( newsid INT PRIMARY KEY, newstitle VARCHAR(255), newscontent TEXT, authorid INT, newsdate TIMESTAMP ); CREATE TABLE newsitem_categories ( newsid INT, categoryid INT ); CREATE TABLE categories ( categoryid INT PRIMARY KEY, categoryname VARCHAR(255) );

14. Combination on Indexing CREATE INDEX newscat_news ON newsitem_categories(newsid); CREATE INDEX newscat_cats ON newsitem_categories(categoryid); CREATE INDEX news_cats ON newsitem_categories(newsid, categoryid); Can we do? YES but LIMITATIONs