inner_join
==========
Inner join the result of functions.

Function Arguments
------------------
.. list-table::
   :widths: 20 10 60
   :header-rows: 1
   :align: left

   * - Name
     - Type
     - Description

   * - functions
     - list
     - The list of the function expression.

   * - index
     - str
     - The index name for inner join.

Description
-----------
``InnerJoin`` combines the result by finding the same index. For example:
Combine them by 'idx'::

  [{'idx': '1', 'foo': 'foo1'}, {'idx': '2', 'foo': 'foo2'}]
  [{'idx': '1', 'bar': 'bar1'}, {'idx': '2', 'bar': 'bar2'}]

becomes::

  [{'idx': '1', 'foo': 'foo1', 'bar': 'bar1'},
   {'idx': '2', 'foo': 'foo2', 'bar': 'bar2'}]