postgresql full text search

1Full Text Searching (or just text search) provides the capability to 
2identify natural-language documents that satisfy a query, and optionally
3to sort them by relevance to the query. The most common type of search is
4to find all documents containing given query terms and return them in
5order of their similarity to the query. Notions of query and similarity 
6are very flexible and depend on the specific application. The simplest
7search considers query as a set of words and similarity as the frequency
8of query words in the document.
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