SQL数据库中日期时间类型，按日期group by 实现

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cast(starttime as date)：  时间转日期类型

实例SQL:

SELECT
COUNT (ID) AS pvNum,
COUNT (DISTINCT userid) AS userNum,
cast(starttime as date) AS staDay
FROM
t_e_visit_record
WHERE true
AND starttime >= '2018-03-20'
GROUP BY
cast(starttime as date)