DateTime按日期和小时分组

SQL Server：

SELECt [activity_dt], count(*)FROM table1GROUP BY DATEPART(day, [activity_dt]), DATEPART(hour, [activity_dt]);

甲骨文：

SELECt [activity_dt], count(*)FROM table1GROUP BY TO_CHAr(activity_dt, 'DD'), TO_CHAr(activity_dt, 'hh');

MySQL的：

SELECt [activity_dt], count(*)FROM table1GROUP BY hour( activity_dt ) , day( activity_dt )