环比：是连续2个单位周期内量的变化比
SELECT
date_format( created_date, '%m' ) AS month,
count( 1 ) AS '数量'
FROM
t_test
WHERE
DATE_FORMAT( created_date, '%Y' ) = '2020'
GROUP BY
month;
同比：是今年某月与去年某月比
SELECT
date_format( created_date, '%Y' ) AS year,
count( 1 ) AS '数量'
FROM
t_test
WHERE
DATE_FORMAT( created_date, '%m') = '07'
GROUP BY
year; 