Do you mean a relational database? If yes, your "search" algorithm is a WHERE clause.

Do you mean contextual search? Lucene is a great search engine implementation written in Java. This might help you marry it with Lucene:

http://www.cabotsolutions.com/2009/05/using-solr-lucene-for-full-text-search-with-mysql-db/

The answer is far more complicated if you're thinking about crawling web sites based on some criteria. Please clarify.

If you are using Microsoft SQL Server, FreeText works very well:

http://msdn.microsoft.com/en-us/library/ms176078.aspx

Let's consider you're using mysql.

Well your question is basically: how to write a query that will search hotel name, food items, and hotel location.

I guess theses 3 informations are stored in 3 different tables. The easiest way would be to simply query the 3 tables one after the other with query like theses:

SELECT * FROM hotel WHERE hotel_name LIKE "%foobar%";
SELECT * FROM hotel_food_item WHERE item_name LIKE "%foobar%";
SELECT * FROM hotel_location WHERE hotel_name LIKE "%foobar%" OR street_name LIKE "%foobar%" OR city LIKE "%foobar%";

• Make sure your search term are safe from SQL injection
• You may (or not) want to group the query into 1 bigger query

If your database is becoming large ( like < 100 000 line per table ), or if you have a lot or search query, you might be interested in creating a search index, or use a dedicated database intend for text search, like elastic search or something else.

Edit: If relevance is a matter, use MATCH AGAINST:

• http://maisonbisson.com/blog/post/10752/making-mysql-do-relevance-ranked-full-text-searches/
• http://www.devshed.com/c/a/PHP/Using-Relevance-Rankings-for-Full-Text-and-Boolean-Searches-with-MySQL/
• PHP MySQL Search And Order By Relevancy

You'll have to create 3 subqueries that do MATCH AGAINST, and them compile them together. You can do AGAINST("foobar") as rank so you'll have the score you needed.

This should look like:

SELECT *
FROM
(
SELECT id, 'hotel' as table_name, MATCH (search_field1) AGAINST ("lorem") as rank FROM tableA
UNION 
SELECT id, 'food' as table_name, MATCH (search_field2) AGAINST ("lorem") as rank FROM tableB
) as res

ORDER BY res.rank DESC

if you are not using innodb table, and instead are using myisam, you can use mysql's built in full text search.

this works by first putting a full-text index on the columns you wish to search, and then creating a query that looks roughly like this:

SELECT *, MATCH(column_to_search) AGAINST($search_string) AS relevance
FROM your_table
WHERE MATCH(keywords) AGAINST($search_string IN BOOLEAN MODE)
ORDER BY relevance
LIMIT 20