Fix Model::first() only use orderBy() when group by is not empty

Author: samsonasik

system/Model.php

@@ -472,8 +472,8 @@ public function first()
 		}
 
 		// Some databases, like PostgreSQL, need order
-		// information to consistently return correct results.
-		if (empty($builder->QBOrderBy) && ! empty($this->primaryKey))
+		// information to consistently return correct results when there is group by
+		if (! empty($this->QBGroupBy) && empty($builder->QBOrderBy) && ! empty($this->primaryKey))
 		{
 			$builder->orderBy($this->table . '.' . $this->primaryKey, 'asc');
 		}

tests/system/Database/Live/ModelTest.php

@@ -251,6 +251,31 @@ public function testFirst()
 
 	//--------------------------------------------------------------------
 
+	public function testFirstWithoutGroupBy()
+	{
+		$model = new UserModel();
+
+		$user = $model->select('SUM(id) as total')
+					  ->where('id >', 2)
+					  ->first();
+		$this->assertEquals(7, $user->total);
+	}
+
+	//--------------------------------------------------------------------
+
+	public function testFirstWithGroupBy()
+	{
+		$model = new UserModel();
+
+		$user = $model->select('SUM(id) as total')
+						->where('id >', 2)
+						->groupBy('id')
+						->first();
+		$this->assertEquals(3, $user->total);
+	}
+
+	//--------------------------------------------------------------------
+
 	public function testFirstRespectsSoftDeletes()
 	{
 		$this->db->table('user')