Most often, Databases have bad designs and are not 
normalized. This can greatly affect the speed of your 
Database. As a general case, learn the 3 Normal Forms and 
apply them at all times. The normal forms above 3rd Normal 
Form are often called de-normalization forms but what this 
really means is that they break some rules to make the 
Database faster.

What I suggest is to stick to the 3rd normal form except if 
you are a DBA (which means you know subsequent forms and 
know what you're doing). Normalization after the 3rd NF is 
often done at a later time, not during design.

for more information go Through below link
http://www.serverwatch.com/tutorials/article.php/2175621

BY USING HINTS,
HASH JOINS,
PARTITION TABLES AND INDEXS, 
RESERVE KEY INDEX, 
BIT MAP INDEX,
COST BASED OPTIMIZATION,
Nested loops,full table scans,query rewrite with 
materialisation views
BASED ON THIS WE OPTIMIZE THE SQL QUERIES.