MDL-83991 tag: Optimized tag sql query

tag/classes/tag.php

@@ -1763,16 +1763,15 @@ class core_tag_tag {
         list($contextsql, $contextsqlparams) = $DB->get_in_or_equal($contextids);
         $params = array_merge($params, $contextsqlparams);
 
-        $subsql = "SELECT DISTINCT t.id
-                    FROM {tag} t
-                    JOIN {tag_instance} ti ON t.id = ti.tagid
-                   WHERE component = ?
-                   AND itemtype = ?
-                   AND contextid {$contextsql}";
+        $subsql = "SELECT DISTINCT ti.tagid
+                     FROM {tag_instance} ti
+                    WHERE ti.component = ?
+                          AND ti.itemtype = ?
+                          AND ti.contextid {$contextsql}";
 
         $sql = "SELECT tt.*
-                FROM ($subsql) tv
-                JOIN {tag} tt ON tt.id = tv.id";
+                  FROM ($subsql) tv
+                  JOIN {tag} tt ON tt.id = tv.tagid";
 
         return array_map(function($record) {
             return new core_tag_tag($record);