Documentation Source Text

  <i>-- that returns the number of space-separated integers contained in its only argument,</i>
  <i>-- the following query could be used to return the titles of the 10 documents that contain</i>
  <i>-- the greatest number of instances of the users query terms. Hopefully, these 10</i>
  <i>-- documents will be those that the users considers more or less the most "relevant".</i>
  SELECT title FROM documents 
    WHERE documents MATCH &lt;query&gt;
    ORDER BY countintegers(offsets(document)) DESC
    OFFSET 0 LIMIT 10
</codeblock>

<p>
  The query above could be made to run faster by using the FTS [matchinfo]
  function to determine the number of query term instances that appear in each
  result. The matchinfo function is much more efficient than the offsets 
  function. Furthermore, the matchinfo function provides extra information

  <i>-- If the application supplies an SQLite user function called "rank" that</i>
  <i>-- interprets the blob of data returned by matchinfo and returns a numeric</i>
  <i>-- relevancy based on it, then the following SQL may be used to return the</i>
  <i>-- titles of the 10 most relevant documents in the dataset for a users query.</i>
  SELECT title FROM documents 
    WHERE documents MATCH &lt;query&gt;
    ORDER BY rank(matchinfo(document)) DESC
    OFFSET 0 LIMIT 10
</codeblock>

<p>
  The SQL query in the example above uses less CPU than the first example
  in this section, but still has a non-obvious performance problem. SQLite
  satisfies this query by retrieving the value of the "title" column and
  matchinfo data from the FTS module for every row matched by the users

<codeblock>
  SELECT title FROM documents JOIN ( 
      SELECT docid, rank(matchinfo(document)) AS rank 
      FROM documents
      WHERE documents MATCH &lt;query&gt;
      ORDER BY rank DESC 
      OFFSET 0 LIMIT 10
  ) AS ranktable USING(docid)
  ORDER BY ranktable.rank DESC
</codeblock>

<p>
  The next block of SQL enhances the query with solutions to two other problems
  that may arise in developing search applications using FTS:

  <i>--      implementation of the rank function has access to the static weight assigned</i>
  <i>--      to each document.</i>
  SELECT title, snippet(documents) FROM documents JOIN ( 
      SELECT docid, rank(matchinfo(document), documents_data.weight) AS rank
      FROM documents JOIN documents_data USING(docid)
      WHERE documents MATCH &lt;query&gt;
      ORDER BY rank DESC 
      OFFSET 0 LIMIT 10
  ) AS ranktable USING(docid)
  WHERE documents MATCH &lt;query&gt;
  ORDER BY ranktable.rank DESC
</codeblock>

<p>
  All the example queries above return the ten most relevant query results.