连续时间问题-sql

问题：con_table(user_id,ttime)  ttime为用户登陆时间，现在需要找出来连续登陆时间天数超过3天的用户

create table con_table (
user_id int not null,
ttime datetime not null);
insert into con_table values (1,'2019-07-07 10:00:01');
insert into con_table values (1,'2019-07-07 11:00:01');
insert into con_table values (1,'2019-07-07 12:00:01');
insert into con_table values (1,'2019-07-08 10:00:01');
insert into con_table values (1,'2019-07-08 11:00:01');
insert into con_table values (1,'2019-07-09 10:00:01');
insert into con_table values (1,'2019-07-11 10:00:01');
insert into con_table values (1,'2019-07-12 10:00:01');
insert into con_table values (1,'2019-07-20 10:00:01');
insert into con_table values (1,'2019-07-21 10:00:01');
insert into con_table values (1,'2019-07-21 11:00:01');
insert into con_table values (1,'2019-07-22 10:00:01');
insert into con_table values (1,'2019-07-23 1