diff --git a/src/Collection.php b/src/Collection.php
index da25b3e..d0dc73b 100644
--- a/src/Collection.php
+++ b/src/Collection.php
@@ -37,6 +37,19 @@ class Collection implements IteratorAggregate, Countable
         return count($this->elements) == 0;
     }
 
+    public function index($index): mixed
+    {
+        if (isset($this->elements[$index])) {
+            return $this->elements[$index];
+        }
+        return null;
+    }
+
+    public function random(): mixed
+    {
+        return array_rand($this->elements);
+    }
+
     public function reduce(callable $fn, mixed $initial): mixed
     {
         return array_reduce($this->elements, $fn, $initial);
diff --git a/src/Expression.php b/src/Expression.php
index 803a024..27d451e 100644
--- a/src/Expression.php
+++ b/src/Expression.php
@@ -25,9 +25,21 @@ class Expression
         if ($operator == "between" && count($this->value) == 2) {
             return "(" . $this->condition . " "  . $this->operator . " ? AND ? )";
         }
+        if ($operator == "notnull") {
+            return "(" . $this->condition . " IS NOT NULL )";
+        }
+        if ($operator == "isnull") {
+            return "(" . $this->condition . " IS NULL )";
+        }
         return "(" . $this->condition . " "  . $this->operator . " ? )";
     }
 
+    public function hasData()
+    {
+        $operator = trim(strtolower($this->operator));
+        return (in_array($operator, ["isnull","notnull"])) ? false : true;
+    }
+
     public function getCondition()
     {
         return $this->condition;
diff --git a/src/QueryBuilder.php b/src/QueryBuilder.php
index ced14e5..c521785 100644
--- a/src/QueryBuilder.php
+++ b/src/QueryBuilder.php
@@ -15,6 +15,7 @@ class QueryBuilder
     protected ?int $take;
     protected ?int $offset;
     protected string $raw_query;
+    protected bool $distinct;
 
     public function __construct($table, $pk = "id", $connection = "default")
     {
@@ -33,6 +34,7 @@ class QueryBuilder
         $this->groupby = [];
         $this->offset = null;
         $this->take = null;
+        $this->distinct = false;
         $this->raw_query = "";
     }
 
@@ -54,6 +56,12 @@ class QueryBuilder
         return $this;
     }
 
+    public function distinct()
+    {
+        $this->distinct = true;
+        return $this;
+    }
+
     public function orderBy($columns, $sort = "ASC")
     {
         if (is_array($columns)) {
@@ -100,6 +108,18 @@ class QueryBuilder
         return $this;
     }
 
+    public function whereNotNull($condition)
+    {
+        $this->wheres[] = new Expression($condition, "notnull", "");
+        return $this;
+    }
+
+    public function whereNull($condition)
+    {
+        $this->wheres[] = new Expression($condition, "isnull", "");
+        return $this;
+    }
+
     public function where($condition, $operator, $value = null)
     {
         if ($value === null) {
@@ -172,7 +192,7 @@ class QueryBuilder
             $model = new Model();
             $ret[] = $model->setPk($this->pk)->setTable($this->table)->fillData($row);
         }
-        return new Collection($ret); 
+        return new Collection($ret);
     }
 
     private function getData(): mixed
@@ -192,7 +212,8 @@ class QueryBuilder
         }
 
         $columns = implode(",", $this->columns);
-        $query = "SELECT " . $columns . " FROM " . $this->table ;
+        $distinct = ($this->distinct) ?  " DISTINCT " : "";
+        $query = "SELECT " . $distinct . " " . $columns . " FROM " . $this->table ;
 
         $where = $this->getWhere();
         $this->fillData($ret);
@@ -213,7 +234,9 @@ class QueryBuilder
     {
         foreach ($this->wheres as $expression) {
             if ($expression instanceof Expression) {
-                $query->addData($expression->getValue());
+                if ($expression->hasData()) {
+                    $query->addData($expression->getValue());
+                }
             }
         }
     }
diff --git a/tests/CollectionTest.php b/tests/CollectionTest.php
index afe80ac..58a443b 100644
--- a/tests/CollectionTest.php
+++ b/tests/CollectionTest.php
@@ -14,6 +14,8 @@ test("collection", function () {
     expect($coll->count())->toBe(11);
     expect($coll->first())->toBe(0);
     expect($coll->last())->toBe(10);
+    expect($coll->index(1))->toBe(1);
+    expect($coll->random())->toBeGreaterThanOrEqual(0)->toBeLessThanOrEqual(11);
 
     $filt = $coll->filter(function($item){ return $item<5;});    
     expect($filt)->toBeInstanceOf(Collection::class);
diff --git a/tests/DbTest.php b/tests/DbTest.php
index 5690a21..727beaa 100644
--- a/tests/DbTest.php
+++ b/tests/DbTest.php
@@ -64,6 +64,14 @@ test("querybuilder", function() {
     $rows = $qb->whereRaw("id = 1")->get();
     expect($rows)->toBeInstanceOf(Collection::class);
     expect(count($rows))->toBe(1);
+
+    $qb->reset();
+    $rows = $qb->distinct()->get();
+    expect(count($rows))->toBe(2);
+
+    $qb->reset();
+    $rows = $qb->whereNotNull("col1")->get();
+    expect(count($rows))->toBe(2);
 });
 
 test("order by", function(){
@@ -91,6 +99,8 @@ test("group by", function(){
     expect($rows->first()->Nb)->toBe(1);
 });
 
+
+
 test("update row", function() {
     $qb = new QueryBuilder("test","id");
     $row = $qb->find(1);
@@ -144,6 +154,22 @@ test("where array", function() {
 
 });
 
+test("is null", function(){
+    $row4 = new Model();
+    $row4->setTable("test");
+    $row4->col1 = null;
+    $row4->date1 = new \DateTime();
+    $ret4 = $row4->save();
+    expect($ret4)->toBe(true);
+
+    $qb = new QueryBuilder("test");
+    $rows = $qb->whereNull("col1")->get();
+
+    expect($rows)->toBeInstanceOf(Collection::class);
+    expect(count($rows))->toBe(1);
+    expect($rows->first()->col1)->toBe(null);
+});
+
 test("second connection", function() {
     $row = new Model();
     $row->setConnection("contwo");