diff --git a/main/gradebook/lib/be/abstractlink.class.php b/main/gradebook/lib/be/abstractlink.class.php
index 9258c0e01e..cb700bff0c 100755
--- a/main/gradebook/lib/be/abstractlink.class.php
+++ b/main/gradebook/lib/be/abstractlink.class.php
@@ -228,6 +228,7 @@ abstract class AbstractLink implements GradebookItem
 
         $result = Database::query($sql);
         $links = AbstractLink::create_objects_from_sql_result($result);
+
         return $links;
     }
 
diff --git a/main/gradebook/lib/be/category.class.php b/main/gradebook/lib/be/category.class.php
index 9f751b6fb6..b704b148ff 100755
--- a/main/gradebook/lib/be/category.class.php
+++ b/main/gradebook/lib/be/category.class.php
@@ -1439,8 +1439,14 @@ class Category implements GradebookItem
                 $sessionId
             );
             if (!empty($subcats)) {
+                /** @var Category $subcat */
                 foreach ($subcats as $subcat) {
-                    $sublinks = $subcat->get_links($stud_id, false, $course_code, $sessionId);
+                    $sublinks = $subcat->get_links(
+                        $stud_id,
+                        false,
+                        $course_code,
+                        $sessionId
+                    );
                     $links = array_merge($links, $sublinks);
                 }
             }
@@ -1567,10 +1573,19 @@ class Category implements GradebookItem
     public static function register_user_certificate($category_id, $user_id)
     {
         // Generating the total score for a course
-        $cats_course = Category::load($category_id, null, null, null, null, api_get_session_id(), false);
-
-        $alleval_course  = $cats_course[0]->get_evaluations($user_id, true);
-        $alllink_course  = $cats_course[0]->get_links($user_id, true);
+        $cats_course = Category::load(
+            $category_id,
+            null,
+            null,
+            null,
+            null,
+            api_get_session_id(),
+            false
+        );
+        /** @var Category $category */
+        $category = $cats_course[0];
+        $alleval_course  = $category->get_evaluations($user_id, true);
+        $alllink_course  = $category->get_links($user_id, true);
         $evals_links = array_merge($alleval_course, $alllink_course);
 
         //@todo move these in a function
diff --git a/main/gradebook/lib/be/exerciselink.class.php b/main/gradebook/lib/be/exerciselink.class.php
index f5b5b1743b..b5d5db16b8 100755
--- a/main/gradebook/lib/be/exerciselink.class.php
+++ b/main/gradebook/lib/be/exerciselink.class.php
@@ -340,14 +340,17 @@ class ExerciseLink extends AbstractLink
         } else {
             $tbl_exercise = $this->get_exercise_table();
         }
-        if ($tbl_exercise=='') {
+
+        $ref_id = intval($this->get_ref_id());
+
+        if ($tbl_exercise == '') {
             return false;
         } elseif (!isset($this->exercise_data)) {
             if ($this->is_hp == 1) {
-                $ref_id = intval($this->get_ref_id());
-                $sql = "SELECT * FROM $tbl_exercise ex, $TBL_ITEM_PROPERTY ip
+                $sql = "SELECT * FROM $tbl_exercise ex
+                        INNER JOIN $TBL_ITEM_PROPERTY ip
+                        ON (ip.ref = ex.id AND ip.c_id = ex.c_id)
                         WHERE
-                            ip.ref = ex.id AND
                             ip.c_id = $this->course_id AND
                             ex.c_id = $this->course_id AND
                             ip.ref = $ref_id AND
@@ -359,7 +362,7 @@ class ExerciseLink extends AbstractLink
                 $sql = 'SELECT * FROM '.$tbl_exercise.'
                         WHERE
                             c_id = '.$this->course_id.' AND
-                            id = '.(int)$this->get_ref_id().' ';
+                            id = '.$ref_id.' ';
             }
             $result = Database::query($sql);
             $this->exercise_data = Database::fetch_array($result);
diff --git a/main/gradebook/lib/flatview_data_generator.class.php b/main/gradebook/lib/flatview_data_generator.class.php
index 5d1011f71b..736411a315 100755
--- a/main/gradebook/lib/flatview_data_generator.class.php
+++ b/main/gradebook/lib/flatview_data_generator.class.php
@@ -163,9 +163,6 @@ class FlatViewDataGenerator
             foreach ($allcat as $sub_cat) {
                 $sub_cat_weight = round(100 * $sub_cat->get_weight() / $main_weight, 1);
                 $add_weight = " $sub_cat_weight %";
-                /*if (isset($this->params['export_pdf']) && $this->params['export_pdf']) {
-                   $add_weight = null;
-                }*/
                 $headers[] = Display::url(
                         $sub_cat->get_name(),
                         api_get_self().'?selectcat='.$sub_cat->get_id()
@@ -190,7 +187,9 @@ class FlatViewDataGenerator
             for ($count = 0; ($count < $items_count) && ($items_start + $count < count($this->evals_links)); $count++) {
                 /** @var AbstractLink $item */
                 $item = $this->evals_links[$count + $items_start];
-                if ($mainCategoryId == $item->get_category_id() && !in_array($item->get_id(), $evaluationsAdded)) {
+                if ($mainCategoryId == $item->get_category_id() &&
+                    !in_array($item->get_id(), $evaluationsAdded)
+                ) {
                     $weight = round(100 * $item->get_weight() / $main_weight, 1);
                     $headers[] = $item->get_name() . ' ' . $weight . ' % ';
                 }