8.执行时间降低到了1.43秒:
| mysql>SELECT DATE(practicetime) date_time,COUNT(DISTINCT a.userid) people_rows FROM USER b straight_join test_log a WHERE a.userid=b.userid AND b.isfree=0 AND LENGTH(b.username)>4 GROUP BY DATE(practicetime); 。。。。。。。 143 rows in set (1.43 sec) |










