diff --git a/main/gradebook/lib/GradebookUtils.php b/main/gradebook/lib/GradebookUtils.php
index a5eda107e7..d02b7ad6ad 100644
--- a/main/gradebook/lib/GradebookUtils.php
+++ b/main/gradebook/lib/GradebookUtils.php
@@ -707,9 +707,12 @@ class GradebookUtils
         $date_certificate
     ) {
         $table = Database::get_main_table(TABLE_MAIN_GRADEBOOK_CERTIFICATE);
-        $sql = 'SELECT COUNT(id) as count
-                FROM '.$table.' gc
-                WHERE gc.cat_id="'.intval($cat_id).'" AND user_id="'.intval($user_id).'" ';
+        $cat_id = (int) $cat_id;
+        $user_id = (int) $user_id;
+
+        $sql = "SELECT COUNT(id) as count
+                FROM $table gc
+                WHERE gc.cat_id = $cat_id AND user_id = $user_id ";
         $rs_exist = Database::query($sql);
         $row = Database::fetch_array($rs_exist);
         if ($row['count'] == 0) {
@@ -734,8 +737,11 @@ class GradebookUtils
     public static function get_certificate_by_user_id($cat_id, $user_id)
     {
         $table = Database::get_main_table(TABLE_MAIN_GRADEBOOK_CERTIFICATE);
-        $sql = 'SELECT * FROM '.$table.'
-                WHERE cat_id="'.intval($cat_id).'" AND user_id="'.intval($user_id).'"';
+        $cat_id = (int) $cat_id;
+        $user_id = (int) $user_id;
+
+        $sql = "SELECT * FROM $table
+                WHERE cat_id = $cat_id AND user_id = $user_id ";
 
         $result = Database::query($sql);
         $row = Database::fetch_array($result, 'ASSOC');
@@ -792,12 +798,12 @@ class GradebookUtils
     ) {
         $user_id = (int) $user_id;
         $table_certificate = Database::get_main_table(TABLE_MAIN_GRADEBOOK_CERTIFICATE);
-        $sql = 'SELECT 
-                    gc.score_certificate, 
-                    gc.created_at, 
-                    gc.path_certificate, 
-                    gc.cat_id, 
-                    gc.user_id, 
+        $sql = 'SELECT
+                    gc.score_certificate,
+                    gc.created_at,
+                    gc.path_certificate,
+                    gc.cat_id,
+                    gc.user_id,
                     gc.id
                 FROM  '.$table_certificate.' gc
                 WHERE gc.user_id = "'.$user_id.'" ';
@@ -849,9 +855,9 @@ class GradebookUtils
 
         //add print header
         if (!$hide_print_button) {
-            $print = '<style>#print_div {               
+            $print = '<style>#print_div {
                 padding:4px;border: 0 none;position: absolute;top: 0px;right: 0px;
-            }            
+            }
             @media print {
                 #print_div  {
                     display: none !important;
@@ -1184,7 +1190,7 @@ class GradebookUtils
                     ";
         } else {
             $sql = 'SELECT user.user_id, user.username, lastname, firstname, official_code
-                    FROM '.$tbl_course_user.' as course_rel_user 
+                    FROM '.$tbl_course_user.' as course_rel_user
                     INNER JOIN '.$tbl_user.' as user
                     ON (course_rel_user.user_id = user.id)
                     WHERE
diff --git a/main/gradebook/lib/be/category.class.php b/main/gradebook/lib/be/category.class.php
index 91df02e12a..e182354a9c 100755
--- a/main/gradebook/lib/be/category.class.php
+++ b/main/gradebook/lib/be/category.class.php
@@ -2131,20 +2131,18 @@ class Category implements GradebookItem
             return false;
         }
 
-        $cattotal = self::load($category_id);
-        $scoretotal = $cattotal[0]->calc_score($user_id);
+        $scoretotal = $category->calc_score($user_id);
 
         // Do not remove this the gradebook/lib/fe/gradebooktable.class.php
         // file load this variable as a global
         $scoredisplay = ScoreDisplay::instance();
-
         $my_score_in_gradebook = $scoredisplay->display_score(
             $scoretotal,
             SCORE_SIMPLE
         );
 
         $my_certificate = GradebookUtils::get_certificate_by_user_id(
-            $category->get_id(),
+            $category_id,
             $user_id
         );
 
@@ -2156,7 +2154,7 @@ class Category implements GradebookItem
                 api_get_utc_datetime()
             );
             $my_certificate = GradebookUtils::get_certificate_by_user_id(
-                $category->get_id(),
+                $category_id,
                 $user_id
             );
         }
diff --git a/main/gradebook/lib/fe/displaygradebook.php b/main/gradebook/lib/fe/displaygradebook.php
index b44948cc0e..19a0c53744 100755
--- a/main/gradebook/lib/fe/displaygradebook.php
+++ b/main/gradebook/lib/fe/displaygradebook.php
@@ -393,7 +393,8 @@ class DisplayGradebook
                 isset($_GET['selectcat']) && $_GET['selectcat'] != 0) &&
                 isset($_GET['studentoverview'])
             ) {
-                $header .= '<td style="vertical-align: top;"><a href="'.api_get_self().'?'.api_get_cidreq().'&studentoverview=&exportpdf=&selectcat='.$catobj->get_id().'" target="_blank">
+                $header .= '<td style="vertical-align: top;">
+                                <a href="'.api_get_self().'?'.api_get_cidreq().'&studentoverview=&exportpdf=&selectcat='.$catobj->get_id().'" target="_blank">
 							 '.Display::return_icon('pdf.png', get_lang('ExportPDF'), [], ICON_SIZE_MEDIUM).'
 							'.get_lang('ExportPDF').'</a>';
             }
@@ -550,17 +551,16 @@ class DisplayGradebook
                 '</a>';
         }
 
-        if (api_is_allowed_to_edit(null, true) || $isCoach) {
+        if ($isCoach || api_is_allowed_to_edit(null, true)) {
             echo $toolbar = Display::toolbarAction(
                 'gradebook-actions',
                 [$actionsLeft, $actionsRight]
             );
         }
 
-        if (api_is_allowed_to_edit(null, true) || $accessToEdit) {
+        if ($accessToEdit || api_is_allowed_to_edit(null, true)) {
             $weight = intval($catobj->get_weight()) > 0 ? $catobj->get_weight() : 0;
             $weight = '<strong>'.get_lang('TotalWeight').' : </strong>'.$weight;
-
             $min_certification = intval($catobj->getCertificateMinScore() > 0) ? $catobj->getCertificateMinScore() : 0;
 
             if (!empty($min_certification)) {
diff --git a/main/inc/lib/certificate.lib.php b/main/inc/lib/certificate.lib.php
index b73e37fcf1..2b1c3b5f84 100755
--- a/main/inc/lib/certificate.lib.php
+++ b/main/inc/lib/certificate.lib.php
@@ -211,6 +211,7 @@ class Certificate extends Model
 
         $params['hide_print_button'] = isset($params['hide_print_button']) ? true : false;
         $categoryId = 0;
+        $my_category = [];
         if (isset($this->certificate_data) && isset($this->certificate_data['cat_id'])) {
             $categoryId = $this->certificate_data['cat_id'];
             $my_category = Category::load($categoryId);
@@ -227,7 +228,6 @@ class Certificate extends Model
             $sessionId = $category->get_session_id();
 
             $skill = new Skill();
-
             $skill->addSkillToUser(
                 $this->user_id,
                 $category,
diff --git a/main/inc/lib/document.lib.php b/main/inc/lib/document.lib.php
index f34da017e5..d261012426 100644
--- a/main/inc/lib/document.lib.php
+++ b/main/inc/lib/document.lib.php
@@ -1835,7 +1835,7 @@ class DocumentManager
     public static function get_default_certificate_id($course_id, $session_id = 0)
     {
         $tbl_category = Database::get_main_table(TABLE_MAIN_GRADEBOOK_CATEGORY);
-        $session_id = intval($session_id);
+        $session_id = (int) $session_id;
         if (empty($session_id)) {
             $session_id = api_get_session_id();
         }
@@ -1843,7 +1843,7 @@ class DocumentManager
         if (empty($session_id)) {
             $sql_session = 'AND (session_id = 0 OR isnull(session_id)) ';
         } elseif ($session_id > 0) {
-            $sql_session = 'AND session_id='.intval($session_id);
+            $sql_session = 'AND session_id='.$session_id;
         } else {
             $sql_session = '';
         }