CREATE INDEX

You can create an index on a table to improve the performance of certain queries.

You can create an index that include one or more columns.
There is a small performance cost in creating an index.
- Your SELECT queries will run dramatically faster.
- Your INSERT, UPDATE and DELETE commands will run slightly slower.
All tables should have a PRIMARY KEY. This will automatically get an index
- There is no point in creating an index that is the same as the primary key.
A typical SELECT .. JOIN query involves a FOREIGN KEY in one table and a PRIMARY KEY in another.
- You should create an index on the FOREIGN KEY to make the join run faster

The table games shows the year and the city hosting the Olympic Games.

games
yr	city
2000	Sydney
2004	Athens
2008	Beijing
2012	London

schema:scott

 DROP TABLE games

 CREATE TABLE games(
  yr INTEGER PRIMARY KEY,
  city VARCHAR(20));
INSERT INTO games VALUES (2000,'Sydney');
INSERT INTO games VALUES (2004,'Athens');
INSERT INTO games VALUES (2008,'Beijing');
INSERT INTO games VALUES (2012,'London');

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