The problem that you are trying to solve is traditional word based search which is probably more suited to a search engine than a SQL database. A typical search engine will allow you to index content such that an efficient word index is created in addition to a relational style table to store the meta-data for each document.
The search engine approach involves indexing the files as a preparation process followed by searching. The indexing part will require that the files are read (spidered) and filtered to extract content and metadata. Once the index is prepared, the search engine's query interface can be used to get reults.
Links to a couple of sites:
http://www.searchtools.com/index.html
http://searchenginewatch.com/