mysql練習50題

轉自在這裏,方便以後複習時進行練習,來源:https://blog.csdn.net/fashion2014/article/details/78826299

表名和字段

–1.學生表
Student(s_id,s_name,s_birth,s_sex) --學生編號,學生姓名, 出生年月,學生性別
–2.課程表
Course(c_id,c_name,t_id) – --課程編號, 課程名稱, 教師編號
–3.教師表
Teacher(t_id,t_name) --教師編號,教師姓名
–4.成績表
Score(s_id,c_id,s_score) --學生編號,課程編號,分數

測試數據(建表語句)

-- 建表
-- 學生表
CREATE TABLE `Student`(
    `s_id` VARCHAR(20),
    `s_name` VARCHAR(20) NOT NULL DEFAULT '',
    `s_birth` VARCHAR(20) NOT NULL DEFAULT '',
    `s_sex` VARCHAR(10) NOT NULL DEFAULT '',
    PRIMARY KEY(`s_id`)
);
-- 課程表
CREATE TABLE `Course`(
    `c_id`  VARCHAR(20),
    `c_name` VARCHAR(20) NOT NULL DEFAULT '',
    `t_id` VARCHAR(20) NOT NULL,
    PRIMARY KEY(`c_id`)
);
-- 教師表
CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20) NOT NULL DEFAULT '',
    PRIMARY KEY(`t_id`)
);
-- 成績表
CREATE TABLE `Score`(
    `s_id` VARCHAR(20),
    `c_id`  VARCHAR(20),
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
);
--插入學生表測試數據
insert into Student values('01' , '趙雷' , '1990-01-01' , '男');
insert into Student values('02' , '錢電' , '1990-12-21' , '男');
insert into Student values('03' , '孫風' , '1990-05-20' , '男');
insert into Student values('04' , '李雲' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吳蘭' , '1992-03-01' , '女');
insert into Student values('07' , '鄭竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
--課程表測試數據
insert into Course values('01' , '語文' , '02');
insert into Course values('02' , '數學' , '01');
insert into Course values('03' , '英語' , '03');
 
--教師表測試數據
insert into Teacher values('01' , '張三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
 
-- 成績表測試數據
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);
題目

1、查詢“01”課程比“02”課程成績高的所有學生的學號;
2、查詢平均成績大於60分的同學的學號和平均成績;
3、查詢所有同學的學號、姓名、選課數、總成績
4、查詢姓“李”的老師的個數;
5、查詢沒學過“張三”老師課的同學的學號、姓名;
6、查詢學過編號“01”並且也學過編號“02”課程的同學的學號、姓名;
7、查詢學過“張三”老師所教的課的同學的學號、姓名;
8、查詢課程編號“01”的成績比課程編號“02”課程低的所有同學的學號、姓名;
9、查詢所有課程成績小於60分的同學的學號、姓名;
10、查詢沒有學全所有課的同學的學號、姓名;
11、查詢至少有一門課與學號爲“01”的同學所學相同的同學的學號和姓名;
12、查詢和"01"號的同學學習的課程完全相同的其他同學的學號和姓名
13、把“SC”表中“張三”老師教的課的成績都更改爲此課程的平均成績;
14、查詢沒學過"張三"老師講授的任一門課程的學生姓名
15、查詢兩門及其以上不及格課程的同學的學號,姓名及其平均成績
16、檢索"01"課程分數小於60,按分數降序排列的學生信息
17、按平均成績從高到低顯示所有學生的平均成績
18、查詢各科成績最高分、最低分和平均分:以如下形式顯示:課程ID,課程name,最高分,最低分,平均分,及格率
19、按各科平均成績從低到高和及格率的百分數從高到低順序
20、查詢學生的總成績並進行排名
21、查詢不同老師所教不同課程平均分從高到低顯示
22、查詢所有課程的成績第2名到第3名的學生信息及該課程成績
23、統計各科成績各分數段人數:課程編號,課程名稱,[100-85],[85-70],[70-60],[0-60]及所佔百分比
24、查詢學生平均成績及其名次
25、查詢各科成績前三名的記錄
26、查詢每門課程被選修的學生數
27、查詢出只選修了一門課程的全部學生的學號和姓名
28、查詢男生、女生人數
29、查詢名字中含有"風"字的學生信息
30、查詢同名同性學生名單,並統計同名人數
31、查詢1990年出生的學生名單(注:Student表中Sage列的類型是datetime)
32、查詢每門課程的平均成績,結果按平均成績升序排列,平均成績相同時,按課程號降序排列
37、查詢不及格的課程,並按課程號從大到小排列
38、查詢課程編號爲"01"且課程成績在60分以上的學生的學號和姓名;
40、查詢選修“張三”老師所授課程的學生中,成績最高的學生姓名及其成績
42、查詢每門功課成績最好的前兩名
43、統計每門課程的學生選修人數(超過5人的課程才統計)。要求輸出課程號和選修人數,查詢結果按人數降序排列,若人數相同,按課程號升序排列
44、檢索至少選修兩門課程的學生學號
45、查詢選修了全部課程的學生信息
46、查詢各學生的年齡
47、查詢本週過生日的學生
48、查詢下週過生日的學生
49、查詢本月過生日的學生
50、查詢下月過生日的學生

答案

-- 1、查詢"01"課程比"02"課程成績高的學生的信息及課程分數	
	
select a.* ,b.s_score as 01_score,c.s_score as 02_score from 
student a 
	join score b on a.s_id=b.s_id and b.c_id='01'
	left join score c on a.s_id=c.s_id and c.c_id='02' or c.c_id = NULL where b.s_score>c.s_score
	
--也可以這樣寫
	select a.*,b.s_score as 01_score,c.s_score as 02_score from student 		  a,score b,score c 
			where a.s_id=b.s_id 
			and a.s_id=c.s_id 
			and b.c_id='01' 
			and c.c_id='02' 
			and b.s_score>c.s_score
-- 2、查詢"01"課程比"02"課程成績低的學生的信息及課程分數
	
select a.* ,b.s_score as 01_score,c.s_score as 02_score from 
	student a left join score b on a.s_id=b.s_id and b.c_id='01' or b.c_id=NULL 
	 join score c on a.s_id=c.s_id and c.c_id='02' where b.s_score<c.s_score
			

-- 3、查詢平均成績大於等於60分的同學的學生編號和學生姓名和平均成績
select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from 
	student b 
	join score a on b.s_id = a.s_id
	GROUP BY b.s_id,b.s_name HAVING avg_score >=60;
	

-- 4、查詢平均成績小於60分的同學的學生編號和學生姓名和平均成績
		-- (包括有成績的和無成績的)
		
select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from 
	student b 
	left join score a on b.s_id = a.s_id
	GROUP BY b.s_id,b.s_name HAVING avg_score <60
	union
select a.s_id,a.s_name,0 as avg_score from 
	student a 
	where a.s_id not in (
				select distinct s_id from score);


-- 5、查詢所有同學的學生編號、學生姓名、選課總數、所有課程的總成績
select a.s_id,a.s_name,count(b.c_id) as sum_course,sum(b.s_score) as sum_score from 
	student a 
	left join score b on a.s_id=b.s_id
	GROUP BY a.s_id,a.s_name;
			
			
-- 6、查詢"李"姓老師的數量 
select count(t_id) from teacher where t_name like '李%';
	
-- 7、查詢學過"張三"老師授課的同學的信息 
select a.* from 
	student a 
	join score b on a.s_id=b.s_id where b.c_id in(
		select c_id from course where t_id =(
			select t_id from teacher where t_name = '張三'));

-- 8、查詢沒學過"張三"老師授課的同學的信息 
select * from 
    student c 
    where c.s_id not in(
        select a.s_id from student a join score b on a.s_id=b.s_id where b.c_id in(
        select a.c_id from course a join teacher b on a.t_id = b.t_id where t_name ='張三'));
-- 9、查詢學過編號爲"01"並且也學過編號爲"02"的課程的同學的信息

select a.* from 
	student a,score b,score c 
	where a.s_id = b.s_id  and a.s_id = c.s_id and b.c_id='01' and c.c_id='02';
	
-- 10、查詢學過編號爲"01"但是沒有學過編號爲"02"的課程的同學的信息
			
select a.* from 
	student a 
	where a.s_id in (select s_id from score where c_id='01' ) and a.s_id not in(select s_id from score where c_id='02')
			

-- 11、查詢沒有學全所有課程的同學的信息 
--@wendiepei的寫法
select s.* from student s 
left join Score s1 on s1.s_id=s.s_id
group by s.s_id having count(s1.c_id)<(select count(*) from course)	
--@k1051785839的寫法
select *
from student
where s_id not in(
select s_id from score t1  
group by s_id having count(*) =(select count(distinct c_id)  from course)) 
-- 12、查詢至少有一門課與學號爲"01"的同學所學相同的同學的信息 

select * from student where s_id in(
	select distinct a.s_id from score a where a.c_id in(select a.c_id from score a where a.s_id='01')
	);
			
-- 13、查詢和"01"號的同學學習的課程完全相同的其他同學的信息 
--@ouyang_1993的寫法
SELECT
 Student.*
FROM
 Student
WHERE
 s_id IN (SELECT s_id FROM Score GROUP BY s_id HAVING COUNT(s_id) = (
    #下面的語句是找到'01'同學學習的課程數
    SELECT COUNT(c_id) FROM Score WHERE s_id = '01'
   )
 )
AND s_id NOT IN (
 #下面的語句是找到學過‘01’同學沒學過的課程,有哪些同學。並排除他們
 SELECT s_id FROM Score
 WHERE c_id IN(
   #下面的語句是找到‘01’同學沒學過的課程
   SELECT DISTINCT c_id FROM Score
   WHERE c_id NOT IN (
     #下面的語句是找出‘01’同學學習的課程
     SELECT c_id FROM Score WHERE s_id = '01'
    )
  ) GROUP BY s_id
) #下面的條件是排除01同學
AND s_id NOT IN ('01')
--@k1051785839的寫法
SELECT
 t3.*
FROM
 (
  SELECT
   s_id,
   group_concat(c_id ORDER BY c_id) group1
  FROM
   score
  WHERE
   s_id &lt;> '01'
  GROUP BY
   s_id
 ) t1
INNER JOIN (
 SELECT
  group_concat(c_id ORDER BY c_id) group2
 FROM
  score
 WHERE
  s_id = '01'
 GROUP BY
  s_id
) t2 ON t1.group1 = t2.group2
INNER JOIN student t3 ON t1.s_id = t3.s_id

-- 14、查詢沒學過"張三"老師講授的任一門課程的學生姓名 
select a.s_name from student a where a.s_id not in (
	select s_id from score where c_id = 
				(select c_id from course where t_id =(
					select t_id from teacher where t_name = '張三')));

-- 15、查詢兩門及其以上不及格課程的同學的學號,姓名及其平均成績 
select a.s_id,a.s_name,ROUND(AVG(b.s_score)) from 
	student a 
	left join score b on a.s_id = b.s_id
	where a.s_id in(
			select s_id from score where s_score<60 GROUP BY  s_id having count(1)>=2)
	GROUP BY a.s_id,a.s_name

-- 16、檢索"01"課程分數小於60,按分數降序排列的學生信息
select a.*,b.c_id,b.s_score from 
	student a,score b 
	where a.s_id = b.s_id and b.c_id='01' and b.s_score<60 ORDER BY b.s_score DESC;
		
-- 17、按平均成績從高到低顯示所有學生的所有課程的成績以及平均成績
select a.s_id,(select s_score from score where s_id=a.s_id and c_id='01') as 語文,
				(select s_score from score where s_id=a.s_id and c_id='02') as 數學,
				(select s_score from score where s_id=a.s_id and c_id='03') as 英語,
			round(avg(s_score),2) as 平均分 from score a  GROUP BY a.s_id ORDER BY 平均分 DESC;
--@喝完這杯還有一箱的寫法
SELECT a.s_id,MAX(CASE a.c_id WHEN '01' THEN a.s_score END ) 語文, 
MAX(CASE a.c_id WHEN '02' THEN a.s_score END ) 數學, 
MAX(CASE a.c_id WHEN '03' THEN a.s_score END ) 英語, 
avg(a.s_score),b.s_name FROM Score a JOIN Student b ON a.s_id=b.s_id GROUP BY a.s_id ORDER BY 5 DESC		
-- 18.查詢各科成績最高分、最低分和平均分:以如下形式顯示:課程ID,課程name,最高分,最低分,平均分,及格率,中等率,優良率,優秀率
--及格爲>=60,中等爲:70-80,優良爲:80-90,優秀爲:>=90
select a.c_id,b.c_name,MAX(s_score),MIN(s_score),ROUND(AVG(s_score),2),
	ROUND(100*(SUM(case when a.s_score>=60 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 及格率,
	ROUND(100*(SUM(case when a.s_score>=70 and a.s_score<=80 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 中等率,
	ROUND(100*(SUM(case when a.s_score>=80 and a.s_score<=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 優良率,
	ROUND(100*(SUM(case when a.s_score>=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 優秀率
	from score a left join course b on a.c_id = b.c_id GROUP BY a.c_id,b.c_name
	
-- 19、按各科成績進行排序,並顯示排名
-- mysql沒有rank函數
	select a.s_id,a.c_id,
        @i:=@i +1 as i保留排名,
        @k:=(case when @score=a.s_score then @k else @i end) as rank不保留排名,
        @score:=a.s_score as score
    from (
        select s_id,c_id,s_score from score GROUP BY s_id,c_id,s_score ORDER BY s_score DESC
)a,(select @k:=0,@i:=0,@score:=0)s
--@k1051785839的寫法
(select * from (select 
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id='01') rank
FROM score t1 where t1.c_id='01'
order by t1.s_score desc) t1)
union
(select * from (select 
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id='02') rank
FROM score t1 where t1.c_id='02'
order by t1.s_score desc) t2)
union
(select * from (select 
t1.c_id,
t1.s_score,
(select count(distinct t2.s_score) from score t2 where t2.s_score>=t1.s_score and t2.c_id='03') rank
FROM score t1 where t1.c_id='03'
order by t1.s_score desc) t3)
-- 20、查詢學生的總成績並進行排名
select a.s_id,
	@i:=@i+1 as i,
	@k:=(case when @score=a.sum_score then @k else @i end) as rank,
	@score:=a.sum_score as score
from (select s_id,SUM(s_score) as sum_score from score GROUP BY s_id ORDER BY sum_score DESC)a,
	(select @k:=0,@i:=0,@score:=0)s
	
-- 21、查詢不同老師所教不同課程平均分從高到低顯示 
		
	select a.t_id,c.t_name,a.c_id,ROUND(avg(s_score),2) as avg_score from course a
		left join score b on a.c_id=b.c_id 
		left join teacher c on a.t_id=c.t_id
		GROUP BY a.c_id,a.t_id,c.t_name ORDER BY avg_score DESC;
-- 22、查詢所有課程的成績第2名到第3名的學生信息及該課程成績
			
			select d.*,c.排名,c.s_score,c.c_id from (
                select a.s_id,a.s_score,a.c_id,@i:=@i+1 as 排名 from score a,(select @i:=0)s where a.c_id='01'  
								ORDER BY a.s_score DESC  
            )c
            left join student d on c.s_id=d.s_id
            where 排名 BETWEEN 2 AND 3
            UNION
            select d.*,c.排名,c.s_score,c.c_id from (
                select a.s_id,a.s_score,a.c_id,@j:=@j+1 as 排名 from score a,(select @j:=0)s where a.c_id='02'  
								ORDER BY a.s_score DESC
            )c
            left join student d on c.s_id=d.s_id
            where 排名 BETWEEN 2 AND 3
            UNION
            select d.*,c.排名,c.s_score,c.c_id from (
                select a.s_id,a.s_score,a.c_id,@k:=@k+1 as 排名 from score a,(select @k:=0)s where a.c_id='03' 
								ORDER BY a.s_score DESC
            )c
            left join student d on c.s_id=d.s_id
            where 排名 BETWEEN 2 AND 3;
			
-- 23、統計各科成績各分數段人數:課程編號,課程名稱,[100-85],[85-70],[70-60],[0-60]及所佔百分比


		select distinct f.c_name,a.c_id,b.`85-100`,b.百分比,c.`70-85`,c.百分比,d.`60-70`,d.百分比,e.`0-60`,e.百分比 from score a
				left join (select c_id,SUM(case when s_score >85 and s_score <=100 then 1 else 0 end) as `85-100`,
											ROUND(100*(SUM(case when s_score >85 and s_score <=100 then 1 else 0 end)/count(*)),2) as 百分比
								from score GROUP BY c_id)b on a.c_id=b.c_id
				left join (select c_id,SUM(case when s_score >70 and s_score <=85 then 1 else 0 end) as `70-85`,
											ROUND(100*(SUM(case when s_score >70 and s_score <=85 then 1 else 0 end)/count(*)),2) as 百分比
								from score GROUP BY c_id)c on a.c_id=c.c_id
				left join (select c_id,SUM(case when s_score >60 and s_score <=70 then 1 else 0 end) as `60-70`,
											ROUND(100*(SUM(case when s_score >60 and s_score <=70 then 1 else 0 end)/count(*)),2) as 百分比
								from score GROUP BY c_id)d on a.c_id=d.c_id
				left join (select c_id,SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end) as `0-60`,
											ROUND(100*(SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end)/count(*)),2) as 百分比
								from score GROUP BY c_id)e on a.c_id=e.c_id
				left join course f on a.c_id = f.c_id
				 
-- 24、查詢學生平均成績及其名次 

		select a.s_id,
				@i:=@i+1 as '不保留空缺排名',
				@k:=(case when @avg_score=a.avg_s then @k else @i end) as '保留空缺排名',
				@avg_score:=avg_s as '平均分'
		from (select s_id,ROUND(AVG(s_score),2) as avg_s from score GROUP BY s_id ORDER BY avg_s DESC)a,(select @avg_score:=0,@i:=0,@k:=0)b;
-- 25、查詢各科成績前三名的記錄
			-- 1.選出b表比a表成績大的所有組
			-- 2.選出比當前id成績大的 小於三個的
		select a.s_id,a.c_id,a.s_score from score a 
			left join score b on a.c_id = b.c_id and a.s_score<b.s_score
			group by a.s_id,a.c_id,a.s_score HAVING COUNT(b.s_id)<3
			ORDER BY a.c_id,a.s_score DESC

-- 26、查詢每門課程被選修的學生數 

		select c_id,count(s_id) from score a GROUP BY c_id

-- 27、查詢出只有兩門課程的全部學生的學號和姓名 
		select s_id,s_name from student where s_id in(
				select s_id from score GROUP BY s_id HAVING COUNT(c_id)=2);

-- 28、查詢男生、女生人數 
		select s_sex,COUNT(s_sex) as 人數  from student GROUP BY s_sex

-- 29、查詢名字中含有"風"字的學生信息

		select * from student where s_name like '%風%';

-- 30、查詢同名同性學生名單,並統計同名人數 
		
		select a.s_name,a.s_sex,count(*) from student a  JOIN 
					student b on a.s_id !=b.s_id and a.s_name = b.s_name and a.s_sex = b.s_sex
		GROUP BY a.s_name,a.s_sex



-- 31、查詢1990年出生的學生名單
		
		select s_name from student where s_birth like '1990%'

-- 32、查詢每門課程的平均成績,結果按平均成績降序排列,平均成績相同時,按課程編號升序排列 

	select c_id,ROUND(AVG(s_score),2) as avg_score from score GROUP BY c_id ORDER BY avg_score DESC,c_id ASC

-- 33、查詢平均成績大於等於85的所有學生的學號、姓名和平均成績 

	select a.s_id,b.s_name,ROUND(avg(a.s_score),2) as avg_score from score a
		left join student b on a.s_id=b.s_id GROUP BY s_id HAVING avg_score>=85
	
-- 34、查詢課程名稱爲"數學",且分數低於60的學生姓名和分數 
	
		select a.s_name,b.s_score from score b join student a on a.s_id=b.s_id where b.c_id=(
					select c_id from course where c_name ='數學') and b.s_score<60

-- 35、查詢所有學生的課程及分數情況; 
	
		
		select a.s_id,a.s_name,
					SUM(case c.c_name when '語文' then b.s_score else 0 end) as '語文',
					SUM(case c.c_name when '數學' then b.s_score else 0 end) as '數學',
					SUM(case c.c_name when '英語' then b.s_score else 0 end) as '英語',
					SUM(b.s_score) as  '總分'
		from student a left join score b on a.s_id = b.s_id 
		left join course c on b.c_id = c.c_id 
		GROUP BY a.s_id,a.s_name


 -- 36、查詢任何一門課程成績在70分以上的姓名、課程名稱和分數; 
			select a.s_name,b.c_name,c.s_score from course b left join score c on b.c_id = c.c_id
				left join student a on a.s_id=c.s_id where c.s_score>=70

		

-- 37、查詢不及格的課程
		select a.s_id,a.c_id,b.c_name,a.s_score from score a left join course b on a.c_id = b.c_id
			where a.s_score<60 
		
--38、查詢課程編號爲01且課程成績在80分以上的學生的學號和姓名; 
		select a.s_id,b.s_name from score a LEFT JOIN student b on a.s_id = b.s_id
			where a.c_id = '01'	and a.s_score>80

-- 39、求每門課程的學生人數 
		select count(*) from score GROUP BY c_id;

-- 40、查詢選修"張三"老師所授課程的學生中,成績最高的學生信息及其成績

		
		-- 查詢老師id	
		select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='張三'
		-- 查詢最高分(可能有相同分數)
		select MAX(s_score) from score where c_id='02'
		-- 查詢信息
		select a.*,b.s_score,b.c_id,c.c_name from student a
			LEFT JOIN score b on a.s_id = b.s_id
			LEFT JOIN course c on b.c_id=c.c_id
			where b.c_id =(select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='張三')
			and b.s_score in (select MAX(s_score) from score where c_id='02')


-- 41、查詢不同課程成績相同的學生的學生編號、課程編號、學生成績 
	select DISTINCT b.s_id,b.c_id,b.s_score from score a,score b where a.c_id != b.c_id and a.s_score = b.s_score
	

-- 42、查詢每門功成績最好的前兩名 
		-- 牛逼的寫法
	select a.s_id,a.c_id,a.s_score from score a
		where (select COUNT(1) from score b where b.c_id=a.c_id and b.s_score>=a.s_score)<=2 ORDER BY a.c_id


-- 43、統計每門課程的學生選修人數(超過5人的課程才統計)。要求輸出課程號和選修人數,查詢結果按人數降序排列,若人數相同,按課程號升序排列  
		select c_id,count(*) as total from score GROUP BY c_id HAVING total>5 ORDER BY total,c_id ASC
		
-- 44、檢索至少選修兩門課程的學生學號 
		select s_id,count(*) as sel from score GROUP BY s_id HAVING sel>=2

-- 45、查詢選修了全部課程的學生信息 
		select * from student where s_id in(		
			select s_id from score GROUP BY s_id HAVING count(*)=(select count(*) from course))


--46、查詢各學生的年齡
	-- 按照出生日期來算,當前月日 < 出生年月的月日則,年齡減一

	select s_birth,(DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(s_birth,'%Y') - 
				(case when DATE_FORMAT(NOW(),'%m%d')>DATE_FORMAT(s_birth,'%m%d') then 0 else 1 end)) as age
		from student;


-- 47、查詢本週過生日的學生
	select * from student where WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))=WEEK(s_birth)
	select * from student where YEARWEEK(s_birth)=YEARWEEK(DATE_FORMAT(NOW(),'%Y%m%d'))
	
	select WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))

-- 48、查詢下週過生日的學生
	select * from student where WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =WEEK(s_birth)

-- 49、查詢本月過生日的學生

	select * from student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d')) =MONTH(s_birth)
	
-- 50、查詢下月過生日的學生
	select * from student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =MONTH(s_birth)


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