SQL语句查询时间过长的优化

Question

下面这段sql

 SELECT
    TT1.COUNT - TT2.COUNT COUNT
FROM
    (
        SELECT
            IFNULL(sum(T.USER_4G_LAST), 0) COUNT
        FROM
            (
                SELECT DISTINCT
                    T1.SITE_CODE,
                    T1.USER_4G_LAST
                FROM
                    BIC_PERF_USER_INFO T1
                WHERE
                    T1.MONTH_STAMP = '201707'
            ) T
    ) TT1,
    (
        SELECT
            IFNULL(sum(T.USER_4G_LAST), 0) COUNT
        FROM
            (
                SELECT DISTINCT
                    T1.SITE_CODE,
                    T1.USER_4G_LAST
                FROM
                    BIC_PERF_USER_INFO T1
                WHERE
                    T1.MONTH_STAMP = '201706'
            ) T
    ) TT2

数据库中数据有150W
所用查询时间需要8秒多,请问有什么方法能够优化这个查询~~~

Answer 1

select IFNULL(sum(T1.USER_4G_LAST), 0) COUNT1 - IFNULL(sum(T2.USER_4G_LAST), 0) COUNT2 as COUNT
from BIC_PERF_USER_INFO T1 , BIC_PERF_USER_INFO T2
where T1.MONTH_STAMP = '201707' and T2.MONTH_STAMP = '201706'