diff --git a/src/Queries/Mysql/Count.php b/src/Queries/Mysql/Count.php
index 5a69a6c..719e49a 100644
--- a/src/Queries/Mysql/Count.php
+++ b/src/Queries/Mysql/Count.php
@@ -11,7 +11,7 @@
  */
 class Count extends BaseQuery
 {
-    use WhereTrait;
+    use WhereExtendedTrait;
     use LimitTrait;
 
     /**
@@ -62,6 +62,7 @@ public function __toString()
     {
         $query = "SELECT COUNT(*) FROM `{$this->entity->table}`";
 
+        $query .= $this->fromToString();
         $query .= $this->whereToString();
         $query .= $this->limitToString();
 
diff --git a/src/Queries/Mysql/LimitTrait.php b/src/Queries/Mysql/LimitTrait.php
index 5e07ac8..515a84c 100644
--- a/src/Queries/Mysql/LimitTrait.php
+++ b/src/Queries/Mysql/LimitTrait.php
@@ -1,7 +1,6 @@
 <?php
 namespace SimpleCrud\Queries\Mysql;
 
-
 /**
  * Common function to manage LIMIT clause
  */
@@ -40,7 +39,7 @@ public function offset($offset)
 
     /**
      * Generate LIMIT clause
-     * 
+     *
      * @return string
      */
     protected function limitToString()
diff --git a/src/Queries/Mysql/Select.php b/src/Queries/Mysql/Select.php
index 1369ad5..93186ab 100644
--- a/src/Queries/Mysql/Select.php
+++ b/src/Queries/Mysql/Select.php
@@ -4,7 +4,6 @@
 use SimpleCrud\Queries\BaseQuery;
 use SimpleCrud\RowCollection;
 use SimpleCrud\Row;
-use SimpleCrud\RowInterface;
 use SimpleCrud\Entity;
 use SimpleCrud\SimpleCrudException;
 use PDOStatement;
@@ -15,75 +14,14 @@
  */
 class Select extends BaseQuery
 {
-    use WhereTrait;
+    use WhereExtendedTrait;
     use LimitTrait;
 
-    protected $fields = [];
-    protected $from = [];
     protected $leftJoin = [];
     protected $orderBy = [];
 
     protected $statement;
 
-    /**
-     * Adds new extra table to the query
-     *
-     * @param string $table
-     *
-     * @return self
-     */
-    public function from($table)
-    {
-        $this->from[] = $table;
-
-        return $this;
-    }
-
-    /**
-     * Adds a WHERE according with the relation of other entity
-     *
-     * @param RowInterface $row
-     * @param string       $through
-     *
-     * @return self
-     */
-    public function relatedWith(RowInterface $row, $through = null)
-    {
-        $entity = $row->getEntity();
-
-        if ($through !== null) {
-            $through = $this->entity->getDb()->$through;
-
-            if (!$through->hasOne($entity)) {
-                throw new SimpleCrudException("The relationship between '{$through->table}' and '{$entity->table}' must be RELATION_HAS_ONE");
-            }
-            if (!$through->hasOne($this->entity)) {
-                throw new SimpleCrudException("The relationship between '{$through->table}' and '{$this->entity->table}' must be RELATION_HAS_ONE");
-            }
-
-            $this->from($through->table);
-            $this->from($entity->table);
-
-            $this->fields[] = "`{$through->table}`.`{$entity->foreignKey}`";
-
-            $this->where("`{$through->table}`.`{$this->entity->foreignKey}` = `{$this->entity->table}`.`id`");
-            $this->where("`{$through->table}`.`{$entity->foreignKey}` = `{$entity->table}`.`id`");
-            $this->where("`{$entity->table}`.`id` IN (:{$through->name})", [":{$through->name}" => $row->get('id')]);
-
-            return $this;
-        }
-
-        if ($this->entity->hasOne($entity)) {
-            return $this->by($entity->foreignKey, $row->get('id'));
-        }
-
-        if ($this->entity->hasMany($entity)) {
-            return $this->byId($row->get($this->entity->foreignKey));
-        }
-
-        throw new SimpleCrudException("The tables {$this->entity->table} and {$entity->table} are no related");
-    }
-
     /**
      * Adds an ORDER BY clause
      *
@@ -159,7 +97,7 @@ public function run()
 
     /**
      * Run the query and return all values
-     * 
+     *
      * @param boolean $idAsKey
      *
      * @return RowCollection
@@ -226,15 +164,9 @@ public function __toString()
             $query .= ', '.static::buildFields($join['entity']->table, array_keys($join['entity']->fields), $join['entity']->name);
         }
 
-        foreach ($this->fields as $field) {
-            $query .= ', '.$field;
-        }
-
+        $query .= $this->fieldsToString();
         $query .= ' FROM `'.$this->entity->table.'`';
-
-        if (!empty($this->from)) {
-            $query .= ', `'.implode('`, `', $this->from).'`';
-        }
+        $query .= $this->fromToString();
 
         foreach ($this->leftJoin as $join) {
             $query .= ' LEFT JOIN `'.$join['entity']->table.'`"';
diff --git a/src/Queries/Mysql/Sum.php b/src/Queries/Mysql/Sum.php
index 56f93cf..bd1f090 100644
--- a/src/Queries/Mysql/Sum.php
+++ b/src/Queries/Mysql/Sum.php
@@ -9,9 +9,9 @@
 /**
  * Manages a database select count query in Mysql databases
  */
-class Count extends BaseQuery
+class Sum extends BaseQuery
 {
-    use WhereTrait;
+    use WhereExtendedTrait;
     use LimitTrait;
 
     protected $field;
@@ -92,6 +92,7 @@ public function __toString()
     {
         $query = "SELECT SUM(`{$this->field}`) FROM `{$this->entity->table}`";
 
+        $query .= $this->fromToString();
         $query .= $this->whereToString();
         $query .= $this->limitToString();
 
diff --git a/src/Queries/Mysql/WhereExtendedTrait.php b/src/Queries/Mysql/WhereExtendedTrait.php
new file mode 100644
index 0000000..15ec254
--- /dev/null
+++ b/src/Queries/Mysql/WhereExtendedTrait.php
@@ -0,0 +1,108 @@
+<?php
+namespace SimpleCrud\Queries\Mysql;
+
+use SimpleCrud\RowInterface;
+
+/**
+ * Common function to manage WHERE clause
+ */
+trait WhereExtendedTrait
+{
+    use WhereTrait;
+
+    protected $from = [];
+    protected $fields = [];
+
+    /**
+     * Adds new extra table to the query
+     *
+     * @param string $table
+     *
+     * @return self
+     */
+    public function from($table)
+    {
+        $this->from[] = $table;
+
+        return $this;
+    }
+
+    /**
+     * Adds a new extra field to the query
+     *
+     * @param string $field
+     *
+     * @return self
+     */
+    public function field($field)
+    {
+        $this->fields[] = $field;
+
+        return $this;
+    }
+
+    /**
+     * Adds a WHERE according with the relation of other entity
+     *
+     * @param RowInterface $row
+     * @param string       $through
+     *
+     * @return self
+     */
+    public function relatedWith(RowInterface $row, $through = null)
+    {
+        $entity = $row->getEntity();
+
+        if ($through !== null) {
+            $through = $this->entity->getDb()->$through;
+
+            if (!$through->hasOne($entity)) {
+                throw new SimpleCrudException("The relationship between '{$through->table}' and '{$entity->table}' must be RELATION_HAS_ONE");
+            }
+            if (!$through->hasOne($this->entity)) {
+                throw new SimpleCrudException("The relationship between '{$through->table}' and '{$this->entity->table}' must be RELATION_HAS_ONE");
+            }
+
+            $this->from($through->table);
+            $this->from($entity->table);
+
+            $this->fields[] = "`{$through->table}`.`{$entity->foreignKey}`";
+
+            $this->where("`{$through->table}`.`{$this->entity->foreignKey}` = `{$this->entity->table}`.`id`");
+            $this->where("`{$through->table}`.`{$entity->foreignKey}` = `{$entity->table}`.`id`");
+            $this->where("`{$entity->table}`.`id` IN (:{$through->name})", [":{$through->name}" => $row->get('id')]);
+
+            return $this;
+        }
+
+        if ($this->entity->hasOne($entity)) {
+            return $this->by($entity->foreignKey, $row->get('id'));
+        }
+
+        if ($this->entity->hasMany($entity)) {
+            return $this->byId($row->get($this->entity->foreignKey));
+        }
+
+        throw new SimpleCrudException("The tables {$this->entity->table} and {$entity->table} are no related");
+    }
+
+    /**
+     * add extra fields to the code
+     *
+     * @return string
+     */
+    protected function fieldsToString($prepend = ', ')
+    {
+        return $this->fields ? $prepend.implode(', ', $this->fields) : '';
+    }
+
+    /**
+     * add extra fields to the code
+     *
+     * @return string
+     */
+    protected function fromToString($prepend = ', ')
+    {
+        return $this->from ? $prepend.'`'.implode('`, `', $this->from).'`' : '';
+    }
+}
diff --git a/src/Queries/Mysql/WhereTrait.php b/src/Queries/Mysql/WhereTrait.php
index 8a2745b..5847822 100644
--- a/src/Queries/Mysql/WhereTrait.php
+++ b/src/Queries/Mysql/WhereTrait.php
@@ -1,7 +1,6 @@
 <?php
 namespace SimpleCrud\Queries\Mysql;
 
-
 /**
  * Common function to manage WHERE clause
  */
@@ -85,7 +84,7 @@ public function byId($id)
 
     /**
      * Generate WHERE clause
-     * 
+     *
      * @return string
      */
     protected function whereToString()
diff --git a/src/Queries/QueryInterface.php b/src/Queries/QueryInterface.php
index b547947..179eac5 100644
--- a/src/Queries/QueryInterface.php
+++ b/src/Queries/QueryInterface.php
@@ -2,7 +2,6 @@
 namespace SimpleCrud\Queries;
 
 use SimpleCrud\Entity;
-use SimpleCrud\SimpleCrudException;
 use PDOStatement;
 
 /**
diff --git a/src/RowCollection.php b/src/RowCollection.php
index ae7dc51..455b762 100644
--- a/src/RowCollection.php
+++ b/src/RowCollection.php
@@ -102,7 +102,7 @@ public function __get($name)
 
     /**
      * Set whether or not use the id as key
-     * 
+     *
      * @param boolean $idAsKey
      *
      * @return self
@@ -135,6 +135,7 @@ public function offsetSet($offset, $value)
 
         if ($this->idAsKey === false) {
             $this->rows[] = $value;
+
             return;
         }
 
diff --git a/tests/RowTest.php b/tests/RowTest.php
index ac5e9bb..8f51209 100644
--- a/tests/RowTest.php
+++ b/tests/RowTest.php
@@ -1,6 +1,5 @@
 <?php
 use SimpleCrud\SimpleCrud;
-use SimpleCrud\Entity;
 
 class RowTest extends PHPUnit_Framework_TestCase
 {