Help with checking data in database

[AlienSector]

I have a query that searchs a specifc column in a table for data and if a match is found, results are presented on entries matching that specific search, however if no search is entered all entries in the database are displayed.

My question is, how would I go about checking the column being searched in the database and if the search text entered is not in the column, it throws out an error stating the item being searched on does not exist in the database?

I know this is probably simple, though I've tried most of what I can and still nothing seems to be working for me right now .


As an example of what I mean, just in case I have confused anyone:

The table name is resources and the column name is keywords (this is the column being searched on). The only entry in the database is vBulletin and the keyword column contains 'vbulletin, forum'. I would like to have a query where if a user searchs on 'community' then an error is shown since community is not a keyword that has been used in the database.

I hope this makes sense. I've been working long hours so I am a bit tired and I know this is a bit jumbled - that's managment for ya!