When you create an index you make it faster to find a particular row. You can also make the JOIN operator faster.

CREATE INDEX gamesIdx ON games(city,yr); SELECT yr, city FROM games
DROP VIEW old_games; DROP INDEX gamesIdx; DROP TABLE games; CREATE TABLE games(yr INT, city VARCHAR(20)); INSERT INTO games(city,yr) VALUES ('Sydney',2000); INSERT INTO games(city,yr) VALUES ('Athens',2004); INSERT INTO games(city,yr) VALUES ('Beijing',2008); INSERT INTO games(city,yr) VALUES ('London',2012);

CREATE INDEX gamesIdx ON games(city,yr);
SELECT yr, city FROM games