<p>I've been experimenting with fulltext search lately and am curious about the meaning of the Score value. For example I have the following query:</p>

<pre><code>SELECT table. * ,
MATCH (
col1, col2, col3
)
AGAINST (
'+(Term1) +(Term1)'
) AS Score
FROM table
WHERE MATCH (
col1, col2, col3
) 
AGAINST (
'+(Term1) +(Term1)'
)
</code></pre>

<p>In the results for Score I've seen results, for one query, between 0.4667041301727 to 11.166275978088. I get that it's MySQLs idea of relevance (the higher the more weight).</p>

<p>What I don't get is how MySQL comes up with that score. Why is the number not returned as a decimal or something besides ? </p>

<p>How come if I run a query "IN BOOLEAN MODE" does the score always return a 1 or a 0 ? Wouldn't all the results be a 1?</p>

<p>Just hoping for some enlightenment. Thanks.</p>

Generally relevance is based on how many matches each row has to the words given to the search.  The exact value will depend on many things, but it really only matters for comparing to other relevance values in the same query.
If you really want the math behind it, you can find it at the
internals manual
.