search: Add result ranking in MySQL

MySQL normally attempts to rank the results when performing a full-
text search. However, this behavior is disabled when using BOOLEAN
MODE. While BOOLEAN MODE is needed in the WHERE clause, the default
NATURAL LANGUAGE MODE can be used in an ORDER BY clause to reenable
ranking.

Bug: T192458
Change-Id: I09462c339432927efead58fb543a10aed2c53195

diff --git a/includes/search/SearchMySQL.php b/includes/search/SearchMySQL.php
index 8e705c1..c98f7e3 100644 (file)
--- a/includes/search/SearchMySQL.php
+++ b/includes/search/SearchMySQL.php
@@ -34,13 +34,13 @@ class SearchMySQL extends SearchDatabase {
        private static $mMinSearchLength;
 
        /**
-        * Parse the user's query and transform it into an SQL fragment which will
-        * become part of a WHERE clause
+        * Parse the user's query and transform it into two SQL fragments:
+        * a WHERE condition and an ORDER BY expression
         *
         * @param string $filteredText
         * @param string $fulltext
         *
-        * @return string
+        * @return array
         */
        function parseQuery( $filteredText, $fulltext ) {
                global $wgContLang;
@@ -127,7 +127,10 @@ class SearchMySQL extends SearchDatabase {
 
                $searchon = $this->db->addQuotes( $searchon );
                $field = $this->getIndexField( $fulltext );
-               return " MATCH($field) AGAINST($searchon IN BOOLEAN MODE) ";
+               return [
+                       " MATCH($field) AGAINST($searchon IN BOOLEAN MODE) ",
+                       " MATCH($field) AGAINST($searchon IN NATURAL LANGUAGE MODE) DESC "
+               ];
        }
 
        function regexTerm( $string, $wildcard ) {
@@ -303,7 +306,8 @@ class SearchMySQL extends SearchDatabase {
                $query['fields'][] = 'page_namespace';
                $query['fields'][] = 'page_title';
                $query['conds'][] = 'page_id=si_page';
-               $query['conds'][] = $match;
+               $query['conds'][] = $match[0];
+               $query['options']['ORDER BY'] = $match[1];
        }
 
        /**
@@ -318,7 +322,7 @@ class SearchMySQL extends SearchDatabase {
                $query = [
                        'tables' => [ 'page', 'searchindex' ],
                        'fields' => [ 'COUNT(*) as c' ],
-                       'conds' => [ 'page_id=si_page', $match ],
+                       'conds' => [ 'page_id=si_page', $match[0] ],
                        'options' => [],
                        'joins' => [],
                ];