SELECT
    MONTHNAME(DATA) AS m,
    sum(valor) AS p

FROM
    despesas

GROUP BY
MONTHNAME(DATA)

----------------------------------------
-  MONTH - SUM DESPESAS - SUM RECEITAS -
- JANUARY - 10432.2     -  103.3       -
- MARCH    - 102.2      -   0          -
- APRIL    - 101.2      -    4         -
----------------------------------------