Every website you create should have a built in search engine.  Google provides a webservice that uses there search engine to search just your site, but if you want more customized search results, you should create your own.

Creating a search engine for your website can be a rabbit hole.  Once you start creating it, you'll find yourself wanting to add more and more features, and making the search results more robust.  It can be hard to know when to just call it good enough.

Deciding on the best approach for creating a site search engine can be some what of a challenge.  There are lots of different ways that you can create a search engine, and there is no one right answer.  If you site is database driven, it is easy and effective to create a search engine using the databases full text search capabilities.  MySQL, MS SQL Server, ORACLE, and I'm sure many of the other relational database management systems provide built in full text search capabilities that are quite robust.

This site is built on a MySQL database, and it's search engine is built using the full text search capabilites of MySQL and the Microsoft Indexing Service for uploaded documents using IXSSO queries through COM+ objects.

Learn how to create a site search engine using MySQL full text search