diff --git a/classes/question/bank/performances_column.php b/classes/question/bank/performances_column.php
index 86b3623b..5ec74497 100644
--- a/classes/question/bank/performances_column.php
+++ b/classes/question/bank/performances_column.php
@@ -151,7 +151,7 @@ public function get_extra_joins() {
                                                         WHERE qasd.name = '-submit'
                                                               AND sq.id = " . $this->studentquizid . "
                                                               AND sqa.userid = " . $this->currentuserid . "
-                                                              AND qas.fraction is not null
+                                                              AND qas.fraction IS NOT NULL
                                                      GROUP BY qa.questionid
                                                      ) qasdmax ON qasd.id = qasdmax.maxqasdid
                                                WHERE qasd.name = '-submit'
@@ -167,13 +167,13 @@ public function get_required_fields() {
         if ($this->studentquiz->aggregated) {
             return array('sp.attempts practice', 'sp.attempts AS myattempts',
                 "(
-                   CASE WHEN sp.attempts is null
+                   CASE WHEN sp.attempts IS NULL
                         THEN ''
                         ELSE CASE WHEN sp.lastanswercorrect = 1
                                   THEN 'gradedright'
                                   ELSE 'gradedwrong'
-                                   END
-                         END
+                        END
+                   END
                  ) AS mylastattempt");
         } else {
             return array('pr.practice', 'myatts.myattempts', 'mylatts.mylastattempt');
diff --git a/classes/question/bank/question_bank_filter.php b/classes/question/bank/question_bank_filter.php
index a1cdf26c..12bed076 100644
--- a/classes/question/bank/question_bank_filter.php
+++ b/classes/question/bank/question_bank_filter.php
@@ -223,7 +223,7 @@ public function get_sql_filter($data) {
                 $params[$name] = "%$value%";
                 break;
             case 1: // Does not contain.
-                $res = ' (searchtag = 0 or searchtag is null) ';
+                $res = ' (searchtag = 0 OR searchtag IS NULL) ';
                 $params[$name] = "%$value%";
                 break;
             case 2: // Equal to.
@@ -239,7 +239,7 @@ public function get_sql_filter($data) {
                 $params[$name] = "%$value";
                 break;
             case 5: // Empty.
-                $res = ' (tags = 0 or tags is null) ';
+                $res = ' (tags = 0 OR tags IS NULL) ';
                 $params[$name] = "-ignore-";
                 break;
             default:
diff --git a/classes/question/bank/tag_column.php b/classes/question/bank/tag_column.php
index 75167406..cf2550e2 100644
--- a/classes/question/bank/tag_column.php
+++ b/classes/question/bank/tag_column.php
@@ -103,7 +103,7 @@ protected function display_content($question, $rowclasses) {
      * @return array sql query join additional
      */
     public function get_extra_joins() {
-        $searchtag = ($this->tagfilteractive) ? "SUM(CASE WHEN t.name LIKE :searchtag then 1 else 0 end)" : "0";
+        $searchtag = ($this->tagfilteractive) ? "SUM(CASE WHEN t.name LIKE :searchtag THEN 1 ELSE 0 END)" : "0";
         return array('tags' => "LEFT JOIN (
                                             SELECT ti.itemid AS questionid, COUNT(*) AS tags, " . $searchtag . " AS searchtag
                                               FROM {tag} t