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~~~