diff --git a/src/Common/Sql.php b/src/Common/Sql.php
index cd02dc3..7ee3a98 100644
--- a/src/Common/Sql.php
+++ b/src/Common/Sql.php
@@ -56,7 +56,8 @@ abstract class Sql {
                 $this->identifier = $identifier;
             }
             
-            public function __toString() {
+            public function __toString() : string
+            {
                 return $this->identifier;
             } 
         };
diff --git a/src/EntityCollection.php b/src/EntityCollection.php
index 1802787..7c6216e 100644
--- a/src/EntityCollection.php
+++ b/src/EntityCollection.php
@@ -222,6 +222,11 @@ class EntityCollection extends \ArrayObject {
         return $list;
     }
 
+    public function sum($field) : float|int
+    {
+        return array_sum($this->column($field));
+    }
+
     public function unique(\Stringable|callable|string $field, bool $strict = false) : self
     {
         $list = [];