06 February 2011

How to develop a search engine using PHP-Part 1?

Today almost all websites have search capability, Using which you can easily search the contents of website by entering some keywords in a text box .So through this post, I will show you how to build a search engine using a keyword based approach. For this, We will use MySQL's extremely powerful full-text search capabilities.

Now you might be wondering about what is Full-Text searching actually?Following points will give you a clear idea about it.

1:-  A Full-Text search makes use of full text indexes. In MySQL it  is an index of type Full-Text.These indexes are set up in specific fields of a table.
2:-  Full-text indexes can be used only with MyISAM tables, and can be created only for CHAR, VARCHAR, or TEXT columns.
3:-  A Full Text index definition can be given in the CREATE TABLE statement when a table is created, or added later using ALTER TABLE or CREATE INDEX.

Basic Features
1:- Full-text searches are faster than other search methods such as wildcard or character based searches, which are commonly performed using MySQL's LIKE command. 
2:- It is ideal for extremely large databases that contain thousands or even millions of rows. Computations are performed faster and rows can be ranked based on search relevance, which is returned as a decimal number by MySQL.

How it is performed?
Full-text searching is performed using MATCH() ... AGAINST syntax. MATCH() takes a comma-separated list that names the columns to be searched. AGAINST takes a string to search for, and an optional modifier that indicates what type of search to perform.

Let us take a simple example
First of all we will create a simple database using command create database ;
Create database manish;
Use manish
Now create a table named data with 3 attributes

    ->   title VARCHAR(200),
    ->   body TEXT,
    ->   FULLTEXT (title,body)
    -> );

Query OK, 0 rows affected (0.00 sec)Here we have set an index on title and body attribute

mysql> INSERT INTO data (title,body) VALUES
    -> ('MySQL Tutorial','DBMS stands for DataBase ...'),
    -> ('How To Use MySQL Well','After you went through a ...'),
    -> ('Optimizing MySQL','In this tutorial we will show ...');

Now let us perform some search using Match()..Against() Keyword. Here there is an important point to be consider,Because full-text searching was designed for larger databases, it is possible for MySQL to return incorrect results when it's used on tables containing smaller amount records

mysql> SELECT * FROM articles
    -> WHERE MATCH (title,body) AGAINST ('database');

| id | title             | body                                     |
|  1 | MySQL Tutorial    | DBMS stands for DataBase ...             |

So here i will  complete the first part of this tutorial ,in next part we will try our hands on some php scripting and will try to implement the actual search engine