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勋章 ①金银铜：在竞赛中获得第一二三名；②好习惯：自然月10天提交；③里程碑：解决1/2/5/10/20/50/100/200题；④每周打卡挑战：完成每周5题，每年1月1日清零。

达成1题里程碑2024-11-29
达成2题里程碑2024-11-29
达成5题里程碑2024-11-29
达成10题里程碑2024-11-29

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评论笔记

评论日期 题目名称 评论内容 站长评论
2024-12-01 HAVING-每次成绩都不低于80分的学生  
妈呀 好荣幸！！但是我要怎么联系到您呢？
 
啥也没说
2024-11-29 HAVING-每次成绩都不低于80分的学生  
想请问一下怎么排除NULL的影响呢？这个NULL是指缺考还是考试不及格呢？
select student_id,max(score) max_score, min(score) min_score, avg(score) avg_score
from scores
where student_id not in(
  select student_id
  from scores
  where score is null)
group by student_id
having min(score)>=80
order by student_id
上面是我写的代码，想请问一下错误原因
 
1、null表示缺考，不参与聚合运算；
2、一个学生在表中记录为80、80、80、null，那么他的平均为80分，而不是60分。他同样符合题意，每次考试都不低于80分。
3、你考虑得很严谨，👍
2024-11-29 不分类别的最火直播间  
where date_format(enter_time,'%Y-%m-%d %H')='2021-09-12 23'
请问一下这个为什么没办法筛选时间呢？
 
如下代码可以通过测试呀，你再试试呢。 SELECT 
    t2.live_id,
    t2.live_nm,
    COUNT(*) AS enter_cnt
FROM 
    ks_live_t1 t1
JOIN 
    ks_live_t2 t2
ON 
    t1.live_id = t2.live_id
WHERE 
    DATE_FORMAT(t1.enter_time, '%Y-%m-%d %H') = '2021-09-12 23'
GROUP BY 
    t1.live_id, t2.live_nm
ORDER BY 
    enter_cnt DESC
LIMIT 5;
2024-11-29 表连接（2）渣男去过我对象没去过，那就用LeftJoin  
一个小问题，题目写到‘探索，渣男经常去，而你男朋友没去过的，究竟是哪些商户呢？’。那应该在表连接之后筛选出渣男去过了，但是男朋友没去过的店铺，这更符合题意吧
select a.mch_nm asshole_tried,a.trx_cnt,b.mch_nm darling_tried
from
(select mch_nm,count(mch_nm) trx_cnt
from cmb_usr_trx_rcd 
where usr_id=5201314520 and year(trx_time) in (2023,2024)
group by mch_nm
having count(mch_nm)>=20) a 
left join 
(select distinct(mch_nm)
from cmb_usr_trx_rcd
where usr_id=5211314521 and year(trx_time)in(2023.2024))b on a.mch_nm=b.mch_nm
where b.mch_nm is null
order by a.trx_cnt desc
 
是的，理论上需要典型的NULL来找出左边有右边没有的

提交记录

提交日期 题目名称 提交代码
2024-11-29 HAVING-每次成绩都不低于80分的学生  
select student_id,max(score) max_score, min(score) min_score, avg(score) avg_score
from scores
group by student_id
having min(score)>=80
order by student_id
2024-11-29 不分类别的最火直播间  
select klt1.live_id,klt2.live_nm,count(distinct klt1.usr_id) enter_cnt
from ks_live_t1 klt1 join ks_live_t2 klt2 using(live_id)
where date_format(klt1.enter_time,'%Y-%m-%d')='2021-09-12' and hour(klt1.enter_time)=23
group by klt1.live_id,klt2.live_nm
order by enter_cnt desc
limit 5
2024-11-29 绘制小时进入人数曲线  
select hour(enter_time) hour_entered, count(*) enter_count
from ks_live_t1
group by hour(enter_time)
order by hour(enter_time)
2024-11-29 表连接（2）渣男去过我对象没去过，那就用LeftJoin  
select a.mch_nm asshole_tried,a.trx_cnt, b.mch_nm darling_tried
from
(select mch_nm,count(mch_nm) trx_cnt 
from cmb_usr_trx_rcd
where usr_id='5201314520'and(year(trx_time) in (2023,2024))
group by mch_nm
having count(mch_nm)>=20) a
left join
(select distinct(mch_nm)
from cmb_usr_trx_rcd
where usr_id='5211314521' and year(trx_time) in(2023,2024)) b
using (mch_nm)
order by trx_cnt desc
2024-11-29 表连接（2）渣男去过我对象没去过，那就用LeftJoin  
select a.mch_nm asshole_tried,a.trx_cnt,b.mch_nm darling_tried
from
(select mch_nm,count(mch_nm) trx_cnt
from cmb_usr_trx_rcd 
where usr_id=5201314520 and year(trx_time) in (2023,2024)
group by mch_nm
having count(mch_nm)>=20) a 
left join 
(select distinct(mch_nm)
from cmb_usr_trx_rcd
where usr_id=5211314521 and year(trx_time)in(2023.2024))b on a.mch_nm=b.mch_nm
order by a.trx_cnt desc
2024-11-29 表连接（2）渣男去过我对象没去过，那就用LeftJoin  
select a.mch_nm asshole_tried,a.trx_cnt,b.mch_nm darling_tried
from
(select mch_nm,count(mch_nm) trx_cnt
from cmb_usr_trx_rcd 
where usr_id=5201314520 and year(trx_time) in (2023,2024)
group by mch_nm
having count(mch_nm)>=20) a 
left join 
(select mch_nm
from cmb_usr_trx_rcd
where usr_id=5211314521 and year(trx_time)in(2023.2024))b on a.mch_nm=b.mch_nm
where b.mch_nm is null
order by a.trx_cnt desc
2024-11-29 表连接（1）你们难道都去过？那就试试用InnerJoin  
select b.mch_nm
from
(select distinct(mch_nm)
from cmb_usr_trx_rcd
where usr_id='5201314520' and year(trx_time)=2024 ) b
join
(select distinct(mch_nm)
from cmb_usr_trx_rcd
where usr_id='5211314521' and year(trx_time)=2024) a
using(mch_nm)
order by mch_nm desc
2024-11-29 表连接（1）你们难道都去过？那就试试用InnerJoin  
select distinct(a.mch_nm)
from cmb_usr_trx_rcd cutr join 
(
select mch_nm
from cmb_usr_trx_rcd
where usr_id=5211314521 and year(trx_time)=2024) aon cutr.mch_nm=a.mch_nm
where cutr.usr_id=5201314520 and year(cutr.trx_time)=2024
order by a.mch_nm desc
2024-11-29 表连接（1）你们难道都去过？那就试试用InnerJoin  
select distinct(a.mch_nm)
from cmb_usr_trx_rcd cutr join 
(
select mch_nm
from cmb_usr_trx_rcd
where usr_id=5201314520 and year(trx_time)=2024) aon cutr.mch_nm=a.mch_nm
where cutr.usr_id=5201314520 and year(cutr.trx_time)=2024
order by a.mch_nm desc
2024-11-29 子查询（1）玩的最嗨那天在做甚？要用Where子查询  
select*
from cmb_usr_trx_rcd
where usr_id=5201314520 and year(trx_time)=2024 and trx_amt=(
select max(trx_amt)
from cmb_usr_trx_rcd
where usr_id=5201314520 and year(trx_time)=2024)
2024-11-29 字符串与通配符（1）名称里面有特服，可以使用通配符  
select count(distinct mch_nm) mch_cnt
from cmb_usr_trx_rcd
where mch_nm like'%按摩保健休闲%'
2024-11-29 分类（1）姿势太多很过分，分类要用CaseWhen  
select a.ser_typ,count(a.ser_typ) trx_cnt,min(date(a.trx_time)) first_date
from(
select *,
(case when trx_amt=288 then '1.WithHand'
when trx_amt=388 then '2.WithMimi'
when trx_amt=588 then '3.BlowJobbie'
when trx_amt=888 then '4.Doi'
when trx_amt=1288 then '5.DoubleFly'
else '6.other'
end )ser_typ
from cmb_usr_trx_rcd) a
where a.usr_id=5201314520 and a.mch_nm='红玫瑰按摩保健休闲'
group by a.ser_typ
order by a.ser_typ;
2024-11-29 分类（1）姿势太多很过分，分类要用CaseWhen  
select
case when trx_amt=288 then '1.WithHand'
when trx_amt=388 then '2.WithMimi'
when trx_amt=588 then '3.BlowJobbie'
when trx_amt=888 then '4.Doi'
when trx_amt=1288 then '5.DoubleFly'
else '6.other'
end as ser_type
,count(1) as trx_cnt
,min(date(trx_time)) as first_date
from 
cmb_usr_trx_rcd
where usr_id='5201314520' and mch_nm='红玫瑰按摩保健休闲'
group by ser_type
order by 1
2024-11-29 分类（1）姿势太多很过分，分类要用CaseWhen  
select a.ser_type,count(a.ser_type) trx_cnt,min(date(a.trx_time)) first_date
from(
select *,
(case when trx_amt=288 then '1.WithHand'
when trx_amt=388 then '2.WithMimi'
when trx_amt=588 then '3.BlowJobbie'
when trx_amt=888 then '4.Doi'
when trx_amt=1288 then '5.DoubleFly'
else '6.other'
end )ser_type
from cmb_usr_trx_rcd) a
where a.usr_id=5201314520 and a.mch_nm='红玫瑰按摩保健休闲'
group by a.ser_type
order by a.ser_type;
2024-11-29 分类（1）姿势太多很过分，分类要用CaseWhen  
select
case when trx_amt=288 then '1.WithHand'
when trx_amt=388 then '2.WithMimi'
when trx_amt=588 then '3.BlowJobbie'
when trx_amt=888 then '4.Doi'
when trx_amt=1288 then '5.DoubleFly'
else '6.other'
end as ser_typ
,count(1) as trx_cnt
,min(date(trx_time)) as first_date
from 
cmb_usr_trx_rcd
where usr_id='5201314520' and mch_nm='红玫瑰按摩保健休闲'
group by ser_typ
order by 1
2024-11-29 分类（1）姿势太多很过分，分类要用CaseWhen  
select a.ser_type,count(a.ser_type) trx_cnt,min(date(a.trx_time)) first_date
from(
select *,
case when trx_amt=288 then '1.WithHand'
when trx_amt=388 then '2.WithMimi'
when trx_amt=588 then '3.BlowJobbie'
when trx_amt=888 then '4.Doi'
when trx_amt=1288 then '5.DoubleFly'
else '6.other'
end ser_type
from cmb_usr_trx_rcd) a
where a.usr_id=5201314520 and a.mch_nm='红玫瑰按摩保健休闲'
group by a.mch_nm,a.ser_type
order by a.ser_type
2024-11-29 分组与聚合函数（6）想知道渣男有多坏，疯狂使用GroupBy  
select usr_id, mch_nm ,sum(trx_amt) trx_amt, count(trx_amt) trx_cnt, min(trx_time) first_time
from cmb_usr_trx_rcd
where usr_id=5201314520 and trx_amt>=288
group by usr_id, mch_nm
order by trx_cnt desc
2024-11-29 分组与聚合函数（6）想知道渣男有多坏，疯狂使用GroupBy  
select usr_id, mch_nm ,sum(trx_amt) trx_amt, count(trx_amt) trx_cnt, min(trx_time) first_time
from cmb_usr_trx_rcd
where usr_id=5201314520
group by usr_id, mch_nm
having sum(trx_amt)>=288
order by trx_cnt desc
2024-11-29 分组与聚合函数（6）想知道渣男有多坏，疯狂使用GroupBy  
select usr_id, mch_nm ,sum(trx_amt) trx_amt, count(trx_amt) trx_cnt, min(trx_time) first_time
from cmb_usr_trx_rcd
where usr_id=5201314520
group by usr_id, mch_nm
order by trx_cnt desc
2024-11-29 分组与聚合函数（5）想知道何时成瘾，用Max Or Min？  
select usr_id,min(trx_time) first_time, mch_nm
from cmb_usr_trx_rcd
where usr_id=5201314520 and mch_nm='红玫瑰按摩保健休闲'
group by usr_id,mch_nm