尝试如下

try like below

select max(degree), Format(date1, "mmm")
from table1
group by Format(date1, "mmm")

SELECT
    DATEADD(month, DATEDIFF(month, 0, t.Date1), 0) AS Date1
    , MAX(degree) AS MaxDegree
FROM
    table1 t
WHERE
    YEAR(t.Date1) IN (2014)
GROUP BY
    DATEADD(month, DATEDIFF(month, 0, t.Date1), 0)