title: SQL Query join 2 tables group by month
body: <p>I have 2 tables 1 named Despesas and other named Receitas, both have the fields
  date, and value.
  I want to sum the value of both grouping by month and year.
  I've tried this</p>
  
  <pre><code>SELECT
      MONTHNAME(DATA) AS m,
      sum(valor) AS p
  
  FROM
      despesas
  
  GROUP BY 
  MONTHNAME(DATA)
  </code></pre>
  
  <p>but i've no idea how to join both in one table like this</p>
  
  <pre><code>----------------------------------------
  -  MONTH - SUM DESPESAS - SUM RECEITAS - 
  - JANUARY - 10432.2     -  103.3       -
  - MARCH    - 102.2      -   0          -
  - APRIL    - 101.2      -    4         -
  ----------------------------------------
  </code></pre>