秦路老师授课，mysql实战部分
use dataanalyst;
SELECT * FROM dataanalyst.orderinfo;
SET SQL_SAFE_UPDATES = 0;
# 将原来的反斜线更改为-
update orderinfo set paidTime = replace(paidTime,'/','-') where paidTime is not null;
# 更新字符串为datatime格式
update orderinfo set paidtime=str_to_date(paidtime,'%Y-%m-%d %H:%i') where paidtime is not null;
# 统计不同月份的下单人数
# 有几个需要注意的点：
# 当有不同的年份时，使用DATE_FORMAT(date,format)
# count()时需要注意有没有重复值
# 未支付isPaid的月份为00,是脏数据，要过滤掉
select month(PaidTime) month,count(distinct(userID)) '总数'
from orderinfo
where isPaid = '已支付'
group by month(PaidTime);
# 统计用户3月份的回购率和复购率
# 复购率：本月消费人数中，有多少人是消费了一次以上
# 回购率：上个月购买，这个月依旧购买
# 编程的时候可以先从简单的写起，一边写一边运行一边改
# 统计所有ID总共有多少，
select count(cu), count(if (cu>1, 1, null)) as "大于一次" ,(count(if (cu>1, 1, null))/count(cu)) "复购率" from(
select userID, count(userID) as cu from orderinfo
where isPaid = "已支付" and month(PaidTime) = 03
# 把多次购买和一次购买区分开
group by userID) t
# 都有谁购买过了，购买了几次
# 回购率
select count(*),count(t3.userID) from(
(select * from orderinfo where month(PaidTime) = 03) a,
(select * from orderinfo where month(PaidTime) = 04) b
)where a.userID = b.userID
select o.userID ,SEX, COUNT(1) from orderinfo o
inner join(
select * from userinfo where sex <> '') t
on o.userID = t.userID
GROUP BY orderID, sex
select count(t1.m), count(t2.m) from
(select userID, date_format(paidTime,'%Y-%m-01') as m from orderinfo
where isPaid = '已支付'
group by userId,date_format(paidTime,'%Y-%m-01')) t1
left join
(select userID, date_format(paidTime,'%Y-%m-01') as m from orderinfo
where isPaid = '已支付'
group by userId,date_format(paidTime,'%Y-%m-01')) t2
on t1.userID = t2.userID
and t1.m = date_sub(t2.m, interval 1 month) # t1的月份= t2的月份 - 一个月
group by t1.m #统计3月份的回购率,以3月份为主要