Home arrow MySQL arrow Page 2 - Optimizing for Query Speed

13.1 Index Optimization and Index Usage - MySQL

Optimzing your queries can help them run more efficiently, which can save a significant amount of time. This article covers index optimization and index usage. It is excerpted from chapter 13 of the MySQL Certification Guide, written by Paul Dubois et al. (Sams, 2005; ISBN: 0672328127).

TABLE OF CONTENTS:
  1. Optimizing for Query Speed
  2. 13.1 Index Optimization and Index Usage
  3. 13.1.2 Obtaining Table Index Information
  4. 13.1.3 Using Indexes
  5. 13.1.3.1 Indexing Column Prefixes
  6. 13.1.3.2 Leftmost Index Prefixes
  7. 13.1.4 FULLTEXT Indexes
By: Sams Publishing
Rating: starstarstarstarstar / 25
August 03, 2006

print this article
SEARCH DEV SHED

TOOLS YOU CAN USE

advertisement

When you create a table, consider whether it should have indexes, because they have important benefits:

  • Indexes contain sorted values. This allows MySQL to find rows containing particular values faster. The effect can be particularly dramatic for joins, which have the potential to require many combinations of rows to be examined.

  • Indexes result in less disk I/O. The server can use an index to go directly to the relevant table records, which reduces the number of records it needs to read. Furthermore, if a query displays information only from indexed columns, MySQL might be able to process it by reading only the indexes and without accessing data rows at all.

13.1.1 Types of Indexes

MySQL supports four types of indexes:

  • A nonunique index is one in which any key value may occur multiple times. This type of index is defined with the keyword INDEX or KEY.

  • A UNIQUE index is unique-valued; that is, every key value is required to be different than all others. (The exception is that NULL values may occur multiple times.)

  • A PRIMARY KEY also is a unique-valued index. It is similar to a UNIQUE index, but has additional restrictions:

    • A table may have multiple UNIQUE indexes, but at most one PRIMARY KEY.

    • A UNIQUE index can contain NULL values, whereas a PRIMARY KEY cannot.

  • A FULLTEXT index is specially designed for text searching.

To define indexes when you're initially creating a table, use CREATE TABLE. To add indexes to an already existing table, use ALTER TABLE or CREATE INDEX. To drop indexes, use ALTER TABLE or DROP INDEX.

ALTER TABLE can add or drop several indexes in the same statement, which is faster than processing each one separately. CREATE INDEX and DROP INDEX allow only one index to be added or dropped at a time.

Index creation using the INDEX, UNIQUE, and PRIMARY KEY keywords is discussed in the "Core Study Guide." FULLTEXT indexes are not covered there because they are a more specialized kind of index. Instead, FULLTEXT indexing is discussed in section 13.1.4, "FULLTEXT Indexes."



 
 
>>> More MySQL Articles          >>> More By Sams Publishing
 

blog comments powered by Disqus
escort Bursa Bursa escort Antalya eskort
   

MYSQL ARTICLES

- Oracle Unveils MySQL 5.6
- MySQL Vulnerabilities Threaten Databases
- MySQL Cloud Options Expand with Google Cloud...
- MySQL 5.6 Prepped to Handle Demanding Web Use
- ScaleBase Service Virtualizes MySQL Databases
- Oracle Unveils MySQL Conversion Tools
- Akiban Opens Database Software for MySQL Use...
- Oracle Fixes MySQL Bug
- MySQL Databases Vulnerable to Password Hack
- MySQL: Overview of the ALTER TABLE Statement
- MySQL: How to Use the GRANT Statement
- MySQL: Creating, Listing, and Removing Datab...
- MySQL: Create, Show, and Describe Database T...
- MySQL Data and Table Types
- McAfee Releases Audit Plugin for MySQL Users

Developer Shed Affiliates

 


Dev Shed Tutorial Topics: