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MySQL 50 题。

MySQL 50 题。

文章目录

数据库。

  1. CREATESCHEMA`new_schema`DEFAULTCHARACTERSET utf8mb4 ;
  3. Operation failed: There was an error while applying the SQL script to the database.
  4. Executing:
  5. CREATESCHEMA`new_schema`DEFAULTCHARACTERSET utf8mb4 ;
  7. ERROR 1044: Access denied foruser'lyfgeek'@'%'todatabase'new_schema'SQL Statement:
  8. CREATESCHEMA`new_schema`DEFAULTCHARACTERSET utf8mb4
  1. CREATESCHEMA`mysql_fifty`DEFAULTCHARACTERSET utf8 ;
  1. CREATETABLE`lyfgeek`.`student`(`id`BIGINTNOTNULLAUTO_INCREMENTCOMMENT'主键 id。',`s_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'学生 id。',`s_name`VARCHAR(45)NOTNULLDEFAULT''COMMENT'姓名。',`s_birth`VARCHAR(45)NOTNULLDEFAULT''COMMENT'出生年月。',`s_sex`VARCHAR(45)NOTNULLDEFAULT''COMMENT'性别。',`db_insert_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPCOMMENT'db_insert_time。',`db_update_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPONUPDATECURRENT_TIMESTAMPCOMMENT'db_update_time。',`db_deleted`INTNOTNULLDEFAULT0COMMENT'db_deleted。',PRIMARYKEY(`id`,`s_id`),UNIQUEINDEX`s_id_UNIQUE`(`s_id`ASC) VISIBLE
  2. )ENGINE=InnoDBDEFAULTCHARACTERSET= utf8mb4
  3.     COMMENT='学生。';-- 课程表。CREATETABLE`lyfgeek`.`course`(`id`BIGINTNOTNULLAUTO_INCREMENTCOMMENT'主键 id。',`c_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'课程 id。',`c_name`VARCHAR(45)NOTNULLDEFAULT''COMMENT'课程名称。',`t_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'教师 id。',`db_insert_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPCOMMENT'db_insert_time。',`db_update_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPONUPDATECURRENT_TIMESTAMPCOMMENT'db_update_time。',`db_deleted`INTNOTNULLDEFAULT0COMMENT'db_deleted。',PRIMARYKEY(`id`),UNIQUEINDEX`c_id_UNIQUE`(`c_id`ASC) VISIBLE
  4. )ENGINE=InnoDBDEFAULTCHARACTERSET= utf8mb4
  5.     COMMENT='成绩。';-- 教师表。CREATETABLE`lyfgeek`.`teacher`(`id`BIGINTNOTNULLAUTO_INCREMENTCOMMENT'主键 id。',`t_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'教师 id。',`t_name`VARCHAR(45)NOTNULLDEFAULT''COMMENT'姓名。',`db_insert_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPCOMMENT'db_insert_time。',`db_update_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPONUPDATECURRENT_TIMESTAMPCOMMENT'db_update_time。',`db_deleted`INTNOTNULLDEFAULT0COMMENT'db_deleted。',PRIMARYKEY(`id`,`t_id`),UNIQUEINDEX`t_id_UNIQUE`(`t_id`ASC) VISIBLE
  6. )ENGINE=InnoDBDEFAULTCHARACTERSET= utf8mb4
  7.     COMMENT='教师。';-- 成绩表。CREATETABLE`lyfgeek`.`score`(`id`BIGINTNOTNULLAUTO_INCREMENTCOMMENT'主键 id。',`s_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'学生 id。',`c_id`VARCHAR(45)NOTNULLDEFAULT''COMMENT'课程 id。',`s_score`INTNULLDEFAULTNULLCOMMENT'成绩。',`db_insert_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPCOMMENT'db_insert_time。',`db_update_time`TIMESTAMPNOTNULLDEFAULTCURRENT_TIMESTAMPONUPDATECURRENT_TIMESTAMPCOMMENT'db_update_time。',`db_deleted`INTNOTNULLDEFAULT0COMMENT'db_deleted。',PRIMARYKEY(`id`))ENGINE=InnoDBDEFAULTCHARACTERSET= utf8mb4
  8.     COMMENT='成绩。';# 学生表测试数据。INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('01','学生 1','2021-01-01','男');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('02','学生 2','2022-02-02','男');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('03','学生 3','2023-03-03','男');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('04','学生 4','2024-04-04','男');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('05','学生 5','2025-05-05','女');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('06','学生 6','2026-06-06','女');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('07','学生 7','2027-07-07','女');INSERTINTO`lyfgeek`.`student`(`s_id`,`s_name`,`s_birth`,`s_sex`)VALUES('08','学生 8','2028-08-08','女');# 课程表测试数据。INSERTINTO`lyfgeek`.`course`(`c_id`,`c_name`,`t_id`)VALUES('01','语文','02');INSERTINTO`lyfgeek`.`course`(`c_id`,`c_name`,`t_id`)VALUES('02','数学','01');INSERTINTO`lyfgeek`.`course`(`c_id`,`c_name`,`t_id`)VALUES('03','英语','03');# 教师表测试数据。INSERTINTO`lyfgeek`.`teacher`(`t_id`,`t_name`)VALUES('01','老师 1');INSERTINTO`lyfgeek`.`teacher`(`t_id`,`t_name`)VALUES('02','老师 2');INSERTINTO`lyfgeek`.`teacher`(`t_id`,`t_name`)VALUES('03','老师 3');# 成绩表测试数据。INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('01','01','80');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('01','02','90');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('01','03','99');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('02','01','70');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('02','02','60');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('02','03','80');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('03','01','80');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('03','02','80');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('03','03','80');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('04','01','50');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('04','02','30');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('04','03','20');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('05','01','76');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('05','02','87');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('06','01','31');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('06','03','34');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('07','02','89');INSERTINTO`lyfgeek`.`score`(`s_id`,`c_id`,`s_score`)VALUES('07','03','98');

sql。

  1. -- 查询课程"01"比课程"02"成绩高的学生的信息及课程分数。-- - in ~ 长型数据变成宽型数据。SELECT st.*,
  2.        t.s01,
  3.        t.s02
  4. FROM(SELECT sc.`s_id`,MAX(CASEWHEN sc.`c_id`='01'THEN sc.`s_score`END) s01,MAX(CASEWHEN sc.`c_id`='02'THEN sc.`s_score`END) s02
  5.       FROM`score` sc
  6.       GROUPBY sc.`s_id`) t,`student` st
  7. WHERE t.s01 > t.s02
  8.   AND t.`s_id`= st.`s_id`;-- 自连接。SELECT st.*,
  9.        sc1.`s_score`,
  10.        sc2.`s_score`FROM`student` st,`score` sc1,`score` sc2
  11. WHERE st.`s_id`= sc1.`s_id`AND sc1.`s_id`= sc2.`s_id`AND sc1.`c_id`='01'AND sc2.`c_id`='02'AND sc1.`s_score`> sc2.`s_score`;-- 2、查询课程"01"比课程"02"成绩低的学生的信息及课程分数。SELECT`student`.*,
  12.        sc1.`s_score`,
  13.        sc2.`s_score`FROM`student`INNERJOIN`score` sc1 ON`student`.`s_id`= sc1.`s_id`AND sc1.`c_id`='01'INNERJOIN`score` sc2 ON sc1.`s_id`= sc2.`s_id`AND sc2.`c_id`='02'WHERE sc1.`s_score`< sc2.`s_score`OR sc1.`s_score`ISNULL;-- 3、查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩。-- 子查询方法。SELECT sc.`s_id`,(SELECT`s_name`FROM`student` st
  14.         WHERE st.`s_id`= sc.`s_id`)AS s_name,AVG(sc.`s_score`)                avg_score
  15. FROM`score` sc
  16. GROUPBY sc.`s_id`HAVING avg_score >=60;-- 两个表连接方法。SELECT st.`s_id`,
  17.        st.`s_name`,AVG(sc.`s_score`)FROM`student` st,`score` sc
  18. WHERE st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGAVG(sc.`s_score`>=60);-- 4、查询平均成绩小于 60 分的同学的学生编号和学生姓名和平均成绩。-- （包括有成绩的和无成绩的）。SELECT st.`s_id`,
  19.        st.`s_name`,AVG(sc.`s_score`)AS avg_score
  20. FROM`student` st,`score` sc
  21. WHERE st.`s_id`= sc.`s_id`GROUPBY sc.`s_id`HAVINGAVG(sc.`s_score`)<60UNIONSELECT st.`s_id`,
  22.        st.`s_name`,0AS avg_score
  23. FROM`student` st
  24. WHERE st.`s_id`NOTIN(SELECTDISTINCT`s_id`FROM`score`);-- 5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩。SELECT st.`s_id`,
  25.        st.`s_name`,COUNT(sc.s_id)AS sum_course,
  26.        IFNULL(SUM(sc.`s_score`),0)AS sum_score
  27. FROM`student` st
  28.          LEFTOUTERJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`;-- 6、查询"李"姓老师的数量。SELECTCOUNT(`t_id`)FROM`teacher`WHERE`t_name`LIKE'李%';-- 7、查询学过"张三"老师授课的同学的信息。SELECT st.*FROM`student` st
  29.          JOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE sc.`c_id`IN(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1'));SELECT st.*FROM`student` st
  30.          INNERJOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE sc.`c_id`IN(SELECT`c_id`FROM`course` c
  31.                              INNERJOIN`teacher` t ON c.`t_id`= t.`t_id`WHERE`t`.`t_name`='老师 1');-- 8、查询没学过"张三"老师授课的同学的信息。SELECT*FROM`student` st
  32. WHERE st.s_id NOTIN(SELECT st.`s_id`FROM`student` st
  33.                                JOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE sc.`c_id`IN(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1')));SELECT*FROM`student`WHERE`s_id`NOTIN(SELECT sc.`s_id`FROM`teacher` t,`score` sc,`course` c
  34.                      WHERE t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND t.`t_name`='老师 1');SELECT*FROM`student`WHERENOTEXISTS(SELECT1FROM(SELECT sc.`s_id`FROM`teacher` t,`score` sc,`course` c
  35.                        WHERE t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND t.`t_name`='老师 1') t
  36.                  WHERE t.s_id = student.s_id);-- 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息。SELECT st.*FROM`student` st,`score` sc1,`score` sc2
  37. WHERE st.`s_id`= sc1.`s_id`AND st.`s_id`= sc2.`s_id`AND sc1.`c_id`='01'AND sc2.`c_id`='02';-- 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息。SELECT st.*FROM`student` st
  38. WHERE st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`c_id`='01')AND st.`s_id`NOTIN(SELECT`s_id`FROM`score`WHERE`c_id`='02');SELECT st.*FROM`student` st,(SELECT`s_id`,MAX(IF(`c_id`='01',`s_score`,NULL)) s01,MAX(IF(`c_id`='02',`s_score`,NULL)) s02
  39.       FROM`score`GROUPBY`s_id`) t
  40. WHERE t.`s_id`= st.`s_id`AND t.s01 ISNOTNULLAND t.s02 ISNULL;-- 11、查询没有学全所有课程的同学的信息。SELECT st.*,COUNT(sc.`c_id`) count_sc
  41. FROM`student` st
  42.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGCOUNT(sc.`c_id`)<(SELECTCOUNT(`c_id`)FROM`course`);SELECT st.*FROM`student` st
  43. WHERE st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`s_id`NOTIN(SELECT sc1.`s_id`FROM`score` sc1
  44.                                                   JOIN`score` sc2 ON sc1.`s_id`= sc2.`s_id`AND sc2.`c_id`='02'JOIN`score` sc3 ON sc1.`s_id`= sc3.`s_id`AND sc3.`c_id`='03'WHERE sc1.`c_id`='01'));-- 12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息。SELECT*FROM`student`WHERE`s_id`IN(SELECTDISTINCT`s_id`FROM`score`WHERE`c_id`IN(SELECT`c_id`FROM`score`WHERE`s_id`='01'))GROUPBY1,2,3,4;-- 第 1 2 3 4 字段。-- 13、查询和"01"号的同学学习的课程完全相同的其他同学的信息。-- 创建 01 所学临时表。CREATETABLE s01_sc_temp ASSELECT t1.*, sc.`c_id` cid2
  45. FROM(SELECT st.*,
  46.              t2.`c_id`FROM`student` st,(SELECT`c_id`FROM`score`WHERE`s_id`='01') t2) t1
  47.          LEFTJOIN`score` sc ON t1.`s_id`= sc.`s_id`AND t1.`c_id`= sc.`c_id`UNIONSELECT t.*,
  48.        sc.`c_id` cid2
  49. FROM(SELECT st.*,
  50.              b.`c_id`FROM`student` st,(SELECT`c_id`FROM`score`WHERE`s_id`='01') b) t
  51.          RIGHTJOIN`score` sc ON t.`s_id`= sc.`s_id`AND t.`c_id`= sc.`c_id`;SELECT*FROM`student`WHERE`s_id`NOTIN(SELECT`s_id`FROM s01_s_temp
  52.                      WHERE cid2 ISNULLOR`c_id`ISNULL)AND`s_id`!='01';-- ~ ~ ~SELECT*FROM`student`WHERE`s_id`IN(SELECTDISTINCT`s_id`FROM`score`WHERE`s_id`!='01'AND`c_id`IN(SELECT`c_id`FROM`score`WHERE`s_id`='01')GROUPBY`s_id`HAVINGCOUNT(1)=(SELECTCOUNT(1)FROM`score`WHERE`s_id`='01'));-- 14、查询没学过"张三"老师讲授的任一门课程的学生姓名。SELECT st.`s_name`FROM`student` st
  53. WHERE st.`s_id`NOTIN(SELECT`s_id`FROM`score`WHERE`c_id`=(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1'))GROUPBY s_id);-- 15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩。SELECT st.`s_id`,
  54.        st.`s_name`,AVG(sc.`s_score`) avg_score
  55. FROM`student` st
  56.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGSUM(IF(sc.`s_score`>=60,0,1))>=2;SELECT st.`s_id`,
  57.        st.`s_name`,AVG(sc.`s_score`) avg_score
  58. FROM`student` st
  59.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGSUM(IF(sc.`s_score`>=60,0,1))>=2;SELECT st.`s_id`,
  60.        st.`s_name`,ROUND(AVG(sc.`s_score`))FROM student st
  61.          LEFTJOIN
  62.      score sc ON st.`s_id`= sc.`s_id`WHERE st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`s_score`<60GROUPBY`s_id`HAVINGCOUNT(1)>=2)GROUPBY st.`s_id`, st.`s_name`;-- 16、检索课程"01"分数小于 60，按分数降序排列的学生信息。SELECT st.*,
  63.        sc.`s_score`FROM`score` sc
  64.          RIGHTJOIN`student` st ON sc.`s_id`= st.`s_id`WHERE sc.`c_id`='01'AND sc.`s_score`<60ORDERBY`s_score`DESC;SELECT st.*,
  65.        sc.`c_id`,
  66.        sc.`s_score`FROM`student` st,`score` sc
  67. WHERE st.`s_id`= sc.`s_id`AND sc.`c_id`='01'AND sc.`s_score`<60ORDERBY sc.`s_score`DESC;-- 17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩。SELECT sc.`s_id`,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='01')AS 语文,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='02')AS 数学,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='03')AS 英语,ROUND(AVG(`s_score`),2)AS 平均分
  68. FROM`score` sc
  69. GROUPBY sc.`s_id`ORDERBY 平均分 DESC;-- 18.查询各科成绩最高分、最低分和平均分，以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率。-- 及格为 >= 60，中等为：70 ~ 80，优良为：80 ~ 90，优秀为：>= 90。SELECT sc.`c_id`,
  70.        c.`c_name`,MAX(`s_score`),MIN(`s_score`),ROUND(AVG(`s_score`),2),ROUND(100*(SUM(IF(sc.`s_score`>=60,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 及格率,ROUND(100*(SUM(IF(sc.`s_score`>=70AND sc.`s_score`<=80,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 中等率,ROUND(100*(SUM(IF(sc.`s_score`>=80AND sc.`s_score`<=90,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 优良率,ROUND(100*(SUM(IF(sc.`s_score`>=90,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 优秀率
  71. FROM`score` sc
  72.          LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`GROUPBY sc.`c_id`, c.`c_name`;-- 19、按各科成绩进行排序，并显示排名（实现不完全）。-- mysql 没有 rank(); 函数。SELECT sc1.`c_id`,
  73.        sc1.`s_id`,
  74.        sc1.`s_score`,COUNT(sc2.`s_score`)+1AS`rank`FROM`score` sc1
  75.          LEFTJOIN`score` sc2 ON sc1.`s_score`< sc2.`s_score`AND sc1.`c_id`= sc2.`c_id`GROUPBY sc1.`c_id`, sc1.`s_id`, sc1.`s_score`ORDERBY sc1.`c_id`,`rank`;-- 20、查询学生的总成绩并进行排名。SELECT t1.`s_id`,@i :=@i+1AS i,@k :=(IF(@score= t1.sum_score,@k,@i))AS`rank`,@score := t1.sum_score                    AS score
  76. FROM(SELECT`s_id`,SUM(`s_score`)AS sum_score
  77.       FROM`score`GROUPBY`s_id`ORDERBY sum_score DESC) t1,(SELECT@k :=0,@i :=0,@score :=0)AS kis;-- 21、查询不同老师所教不同课程平均分从高到低显示。SELECT c.`t_id`,
  78.        t.`t_name`,
  79.        c.`c_id`,ROUND(AVG(`s_score`),2)AS avg_score
  80. FROM`course` c
  81.          LEFTJOIN`score` sc ON c.`c_id`= sc.`c_id`LEFTJOIN`teacher` t ON c.`t_id`= t.`t_id`GROUPBY c.`c_id`, c.`t_id`, t.`t_name`ORDERBY avg_score DESC;-- 22、查询所有课程的成绩第 2 名到第 3 名的学生信息及该课程成绩。SELECT d.*,
  82.        si2.排名,
  83.        si2.`s_score`,
  84.        si2.`c_id`FROM(SELECT sc.`s_id`,
  85.              sc.`s_score`,
  86.              sc.`c_id`,@i :=@i+1AS 排名
  87.       FROM`score` sc,(SELECT@i :=0)as i2
  88.       WHERE sc.c_id ='01')as si2
  89.          LEFTJOIN
  90.      student d ON si2.s_id = d.s_id
  91. WHERE 排名 BETWEEN2AND3UNIONSELECT st.*,
  92.        sj2.排名,
  93.        sj2.s_score,
  94.        sj2.c_id
  95. FROM(SELECT sc.s_id,
  96.              sc.s_score,
  97.              sc.c_id,@j :=@j+1AS 排名
  98.       FROM`score` sc,(SELECT@j :=0)as j2
  99.       WHERE sc.c_id ='02')as sj2
  100.          LEFTJOIN`student` st ON sj2.s_id = st.s_id
  101. WHERE 排名 BETWEEN2AND3UNIONSELECT d.*,
  102.        s.排名,
  103.        s.`s_score`,
  104.        s.`c_id`FROM(SELECT sc.`s_id`,
  105.              sc.`s_score`,
  106.              sc.`c_id`,@k :=@k+1AS 排名
  107.       FROM`score` sc,(SELECT@k :=0)as k2
  108.       WHERE sc.`c_id`='03')as s
  109.          LEFTJOIN`student` d ON s.`s_id`= d.`s_id`WHERE 排名 BETWEEN2AND3;-- 23、统计各科成绩各分数段人数：课程编号, 课程名称, [100-85], [85-70], [70-60], [0-60] 及所占百分比。SELECTDISTINCT c.`c_name`,
  110.                 sc.`c_id`,
  111.                 t1.`85-100`,
  112.                 t1.百分比,
  113.                 t2.`70-85`,
  114.                 t2.百分比,
  115.                 t3.`60-70`,
  116.                 t3.百分比,
  117.                 t4.`0-60`,
  118.                 t4.百分比
  119. FROM`score` sc
  120.          LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>85AND`s_score`<=100,1,0))AS`85-100`,ROUND(100*(SUM(IF(`s_score`>85AND`s_score`<=100,1,0))/COUNT(*)),2)AS 百分比
  121.       FROM`score`GROUPBY`c_id`) t1 ON sc.`c_id`= t1.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>70AND`s_score`<=85,1,0))AS`70-85`,ROUND(100*(SUM(IF(`s_score`>70AND`s_score`<=85,1,0))/COUNT(*)),2)AS 百分比
  122.       FROM`score`GROUPBY`c_id`) t2 ON sc.`c_id`= t2.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>60AND`s_score`<=70,1,0))AS`60-70`,ROUND(100*(SUM(IF(`s_score`>60AND`s_score`<=70,1,0))/COUNT(*)),2)AS 百分比
  123.       FROM`score`GROUPBY`c_id`) t3 ON sc.`c_id`= t3.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>=0AND`s_score`<=60,1,0))AS`0-60`,ROUND(100*(SUM(IF(`s_score`>=0AND`s_score`<=60,1,0))/COUNT(*)),2)AS 百分比
  124.       FROM`score`GROUPBY`c_id`) t4 ON sc.`c_id`= t4.`c_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`;-- 24、查询学生平均成绩及其名次。SELECT t.`s_id`,@i :=@i+1AS'不保留空缺排名',@k :=(IF(@avg_score= t.avg_score,@k,@i))AS'保留空缺排名',@avg_score := avg_score                      AS'平均分'FROM(SELECT`s_id`,ROUND(AVG(`s_score`),2)AS avg_score
  125.       FROM score
  126.       GROUPBY`s_id`) t,(SELECT@avg_score :=0,@i :=0,@k :=0) b;-- 25、查询各科成绩前三名的记录。-- - 选出 sc1 表比 sc2 表成绩大的所有组。-- - 选出比当前 id 成绩大的小于三个的。SELECT sc1.`s_id`,
  127.        sc1.`c_id`,
  128.        sc1.`s_score`FROM`score` sc1
  129.          LEFTJOIN`score` sc2 ON sc1.`c_id`= sc2.`c_id`AND sc1.`s_score`< sc2.`s_score`GROUPBY sc1.`s_id`, sc1.`c_id`, sc1.`s_score`HAVINGCOUNT(sc2.`s_id`)<3ORDERBY sc1.`c_id`, sc1.`s_score`DESC;-- 26、查询每门课程被选修的学生数。SELECT`c_id`,COUNT(`s_id`)FROM`score`GROUPBY`c_id`;-- 27、查询出只有两门课程的全部学生的学号和姓名。SELECT`s_id`,`s_name`FROM`student`WHERE`s_id`IN(SELECT`s_id`FROM`score`GROUPBY`s_id`HAVINGCOUNT(`c_id`)=2);-- 28、查询男生、女生人数。SELECT`s_sex`,COUNT(`s_sex`)AS 人数
  130. FROM student
  131. GROUPBY s_sex;-- 29、查询名字中含有"风"字的学生信息。SELECT*FROM`student`WHERE`s_name`LIKE'%风%';-- 30、查询同名同性学生名单，并统计同名人数。SELECT st1.`s_name`,
  132.        st1.`s_sex`,COUNT(*)FROM`student` st1
  133.          JOIN`student` st2 ON st1.`s_id`!= st2.`s_id`AND st1.`s_name`= st2.`s_name`AND st1.`s_sex`= st2.`s_sex`GROUPBY st1.`s_name`, st1.`s_sex`;-- 31、查询 1990 年出生的学生名单。SELECT`s_name`FROM`student`WHERE`s_birth`LIKE'1990%';-- 32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列。SELECT`c_id`,ROUND(AVG(`s_score`),2)AS avg_score
  134. FROM`score`GROUPBY`c_id`ORDERBY avg_score DESC,`c_id`ASC;-- 33、查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩。SELECT sc.`s_id`,
  135.        st.`s_name`,ROUND(AVG(sc.`s_score`),2)AS avg_score
  136. FROM`score` sc
  137.          LEFTJOIN`student` st ON sc.`s_id`= st.`s_id`GROUPBY`s_id`HAVING avg_score >=85;-- 34、查询课程名称为"数学"，且分数低于 60 的学生姓名和分数。SELECT st.`s_name`,
  138.        sc.`s_score`FROM`score` sc
  139.          LEFTJOIN`student` st ON st.`s_id`= sc.`s_id`WHERE sc.`c_id`=(SELECT`c_id`FROM`course`WHERE`c_name`='数学')AND sc.s_score <60;-- 35、查询所有学生的课程及分数情况。SELECT st.`s_id`,
  140.        st.`s_name`,SUM(IF(c.`c_name`='语文', sc.`s_score`,0))AS'语文',SUM(IF(c.`c_name`='数学', sc.`s_score`,0))AS'数学',SUM(IF(c.`c_name`='英语', sc.`s_score`,0))AS'英语',SUM(sc.`s_score`)AS'总分'FROM`student` st
  141.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`GROUPBY st.`s_id`, st.`s_name`;-- 36、查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数。SELECT st.`s_name`,
  142.        c.`c_name`,
  143.        sc.`s_score`FROM`course` c
  144.          LEFTJOIN`score` sc ON c.`c_id`= sc.`c_id`LEFTJOIN`student` st ON st.`s_id`= sc.`s_id`WHERE sc.`s_score`>=70;-- 37、查询不及格的课程。SELECT sc.`s_id`,
  145.        sc.`c_id`,
  146.        c.`c_name`,
  147.        sc.`s_score`FROM`score` sc
  148.          LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`WHERE sc.`s_score`<60;-- 38、查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名。SELECT sc.`s_id`,
  149.        st.`s_name`FROM`score` sc
  150.          LEFTJOIN`student` st ON sc.`s_id`= st.`s_id`WHERE sc.`c_id`='01'AND sc.`s_score`>80;-- 39、求每门课程的学生人数。SELECTCOUNT(*)FROM`score`GROUPBY`c_id`;-- 40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩。-- 查询老师 id。SELECT`c_id`FROM`course` c,`teacher` t
  151. WHERE c.`t_id`= t.`t_id`AND t.`t_name`='老师 1';-- 查询最高分（可能有相同分数）。SELECTMAX(`s_score`)FROM`score`WHERE`c_id`='02';-- 查询信息。SELECT st.*,
  152.        sc.`s_score`,
  153.        sc.`c_id`,
  154.        c.`c_name`FROM`student` st
  155.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`WHERE sc.`c_id`=(SELECT`c_id`FROM`course` c,`teacher` t
  156.                    WHERE c.`t_id`= t.`t_id`AND t.`t_name`='老师 1')AND sc.s_score IN(SELECTMAX(s_score)FROM score
  157.                      WHERE c_id ='02');SELECT c.`c_name`, sc.`s_score`, st.*FROM`course` c,`score` sc,`teacher` t,`student` st
  158. WHERE t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND st.`s_id`= sc.`s_id`AND t.`t_name`='老师 1'AND sc.`s_score`IN(SELECTMAX(`s_score`)FROM`course`,`score`,`teacher`,`student`WHERE`teacher`.`t_id`=`course`.`t_id`AND`course`.`c_id`=`score`.`c_id`AND`student`.`s_id`=`score`.`s_id`AND`teacher`.`t_name`='老师 1');-- 41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩。SELECTDISTINCT sc2.`s_id`,
  159.                 sc2.`c_id`,
  160.                 sc2.`s_score`FROM`score` sc1,`score` sc2
  161. WHERE sc1.`c_id`!= sc2.`c_id`AND sc1.`s_score`= sc2.`s_score`;-- 42、查询每门功成绩最好的前两名。-- 牛逼的写法。SELECT sc1.`s_id`,
  162.        sc1.`c_id`,
  163.        sc1.`s_score`FROM`score` sc1
  164. WHERE(SELECTCOUNT(1)FROM`score` sc2
  165.        WHERE sc2.`c_id`= sc1.`c_id`AND sc2.`s_score`>= sc1.`s_score`)<=2ORDERBY sc1.`c_id`;-- 43、统计每门课程的学生选修人数（超过 5 人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列。SELECT`c_id`,COUNT(*)AS total
  166. FROM`score`GROUPBY`c_id`HAVING total >5ORDERBY total DESC,`c_id`;-- 44、检索至少选修两门课程的学生学号。SELECT`s_id`,COUNT(*)FROM`score`GROUPBY`s_id`HAVINGCOUNT(*)>=2;-- 45、查询选修了全部课程的学生信息。SELECT*FROM`student`WHERE`s_id`IN(SELECT`s_id`FROM`score`GROUPBY`s_id`HAVINGCOUNT(*)=(SELECTCOUNT(*)FROM`course`));-- 46、查询各学生的年龄。-- 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一。SELECT`s_birth`,(DATE_FORMAT(NOW(),'%Y')- DATE_FORMAT(`s_birth`,'%Y')-(IF(DATE_FORMAT(NOW(),'%m%d')> DATE_FORMAT(`s_birth`,'%m%d'),0,1)))AS age
  167. FROM`student`;-- 47、查询本周过生日的学生。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、查询下周过生日的学生。SELECT*FROM`student`WHERE WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1= WEEK(`s_birth`);-- 49、查询本月过生日的学生。SELECT*FROM`student`WHEREMONTH(DATE_FORMAT(NOW(),'%Y%m%d'))=MONTH(`s_birth`);-- 50、查询下月过生日的学生。SELECT*FROM`student`WHEREMONTH(DATE_FORMAT(NOW(),'%Y-%m-%d'))+1=MONTH(`s_birth`);
  1. -- 查询课程"01"比课程"02"成绩高的学生的信息及课程分数。-- - in ~ 长型数据变成宽型数据。SELECT 
  2.     st.*, t.s01, t.s02
  3. FROM(SELECT 
  4.         sc.`s_id`,MAX(CASEWHEN sc.`c_id`='01'THEN sc.`s_score`END) s01,MAX(CASEWHEN sc.`c_id`='02'THEN sc.`s_score`END) s02
  5.     FROM`score` sc
  6.     GROUPBY sc.`s_id`) t,`student` st
  7. WHERE
  8.     t.s01 > t.s02 AND t.`s_id`= st.`s_id`;-- 自连接。SELECT 
  9.     st.*, sc1.`s_score`, sc2.`s_score`FROM`student` st,`score` sc1,`score` sc2
  10. WHERE
  11.     st.`s_id`= sc1.`s_id`AND sc1.`s_id`= sc2.`s_id`AND sc1.`c_id`='01'AND sc2.`c_id`='02'AND sc1.`s_score`> sc2.`s_score`;-- 2、查询课程"01"比课程"02"成绩低的学生的信息及课程分数。SELECT`student`.*, sc1.`s_score`, sc2.`s_score`FROM`student`INNERJOIN`score` sc1 ON`student`.`s_id`= sc1.`s_id`AND sc1.`c_id`='01'INNERJOIN`score` sc2 ON sc1.`s_id`= sc2.`s_id`AND sc2.`c_id`='02'WHERE
  12.     sc1.`s_score`< sc2.`s_score`OR sc1.`s_score`ISNULL;-- 3、查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩。-- 子查询方法。SELECT 
  13.     sc.`s_id`,(SELECT`s_name`FROM`student` st
  14.         WHERE
  15.             st.`s_id`= sc.`s_id`)AS s_name,AVG(sc.`s_score`) avg_score
  16. FROM`score` sc
  17. GROUPBY sc.`s_id`HAVING avg_score >=60;-- 两个表连接方法。SELECT 
  18.     st.`s_id`, st.`s_name`,AVG(sc.`s_score`)FROM`student` st,`score` sc
  19. WHERE
  20.     st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGAVG(sc.`s_score`>=60);-- 4、查询平均成绩小于 60 分的同学的学生编号和学生姓名和平均成绩。-- （包括有成绩的和无成绩的）。SELECT 
  21.     st.`s_id`, st.`s_name`,AVG(sc.`s_score`)AS avg_score
  22. FROM`student` st,`score` sc
  23. WHERE
  24.     st.`s_id`= sc.`s_id`GROUPBY sc.`s_id`HAVINGAVG(sc.`s_score`)<60UNIONSELECT 
  25.     st.`s_id`, st.`s_name`,0AS avg_score
  26. FROM`student` st
  27. WHERE
  28.     st.`s_id`NOTIN(SELECTDISTINCT`s_id`FROM`score`);-- 5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩。SELECT 
  29.     st.`s_id`,
  30.     st.`s_name`,COUNT(sc.s_id)AS sum_course,
  31.     IFNULL(SUM(sc.`s_score`),0)AS sum_score
  32. FROM`student` st
  33.         LEFTOUTERJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`;-- 6、查询"李"姓老师的数量。SELECTCOUNT(`t_id`)FROM`teacher`WHERE`t_name`LIKE'李%';-- 7、查询学过"张三"老师授课的同学的信息。SELECT 
  34.     st.*FROM`student` st
  35.         JOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE
  36.     sc.`c_id`IN(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1'));SELECT 
  37.     st.*FROM`student` st
  38.         INNERJOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE
  39.     sc.`c_id`IN(SELECT`c_id`FROM`course` c
  40.                 INNERJOIN`teacher` t ON c.`t_id`= t.`t_id`WHERE`t`.`t_name`='老师 1');-- 8、查询没学过"张三"老师授课的同学的信息。SELECT*FROM`student` st
  41. WHERE
  42.     st.s_id NOTIN(SELECT 
  43.             st.`s_id`FROM`student` st
  44.                 JOIN`score` sc ON st.`s_id`= sc.`s_id`WHERE
  45.             sc.`c_id`IN(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1')));SELECT*FROM`student`WHERE`s_id`NOTIN(SELECT 
  46.             sc.`s_id`FROM`teacher` t,`score` sc,`course` c
  47.         WHERE
  48.             t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND t.`t_name`='老师 1');SELECT*FROM`student`WHERENOTEXISTS(SELECT1FROM(SELECT 
  49.                 sc.`s_id`FROM`teacher` t,`score` sc,`course` c
  50.             WHERE
  51.                 t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND t.`t_name`='老师 1') t
  52.         WHERE
  53.             t.s_id = student.s_id);-- 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息。SELECT 
  54.     st.*FROM`student` st,`score` sc1,`score` sc2
  55. WHERE
  56.     st.`s_id`= sc1.`s_id`AND st.`s_id`= sc2.`s_id`AND sc1.`c_id`='01'AND sc2.`c_id`='02';-- 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息。SELECT 
  57.     st.*FROM`student` st
  58. WHERE
  59.     st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`c_id`='01')AND st.`s_id`NOTIN(SELECT`s_id`FROM`score`WHERE`c_id`='02');SELECT 
  60.     st.*FROM`student` st,(SELECT`s_id`,MAX(IF(`c_id`='01',`s_score`,NULL)) s01,MAX(IF(`c_id`='02',`s_score`,NULL)) s02
  61.     FROM`score`GROUPBY`s_id`) t
  62. WHERE
  63.     t.`s_id`= st.`s_id`AND t.s01 ISNOTNULLAND t.s02 ISNULL;-- 11、查询没有学全所有课程的同学的信息。SELECT 
  64.     st.*,COUNT(sc.`c_id`) count_sc
  65. FROM`student` st
  66.         LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGCOUNT(sc.`c_id`)<(SELECTCOUNT(`c_id`)FROM`course`);SELECT 
  67.     st.*FROM`student` st
  68. WHERE
  69.     st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`s_id`NOTIN(SELECT 
  70.                     sc1.`s_id`FROM`score` sc1
  71.                         JOIN`score` sc2 ON sc1.`s_id`= sc2.`s_id`AND sc2.`c_id`='02'JOIN`score` sc3 ON sc1.`s_id`= sc3.`s_id`AND sc3.`c_id`='03'WHERE
  72.                     sc1.`c_id`='01'));-- 12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息。SELECT*FROM`student`WHERE`s_id`IN(SELECTDISTINCT`s_id`FROM`score`WHERE`c_id`IN(SELECT`c_id`FROM`score`WHERE`s_id`='01'))GROUPBY1,2,3,4;-- 第 1 2 3 4 字段。-- 13、查询和"01"号的同学学习的课程完全相同的其他同学的信息。-- 创建 01 所学临时表。CREATETABLE s01_sc_temp ASSELECT t1.*, sc.`c_id` cid2 FROM(SELECT 
  73.         st.*, t2.`c_id`FROM`student` st,(SELECT`c_id`FROM`score`WHERE`s_id`='01') t2) t1
  74.         LEFTJOIN`score` sc ON t1.`s_id`= sc.`s_id`AND t1.`c_id`= sc.`c_id`UNIONSELECT 
  75.     t.*, sc.`c_id` cid2
  76. FROM(SELECT 
  77.         st.*, b.`c_id`FROM`student` st,(SELECT`c_id`FROM`score`WHERE`s_id`='01') b) t
  78.         RIGHTJOIN`score` sc ON t.`s_id`= sc.`s_id`AND t.`c_id`= sc.`c_id`;SELECT*FROM`student`WHERE`s_id`NOTIN(SELECT`s_id`FROM
  79.             s01_s_temp
  80.         WHERE
  81.             cid2 ISNULLOR`c_id`ISNULL)AND`s_id`!='01';-- ~ ~ ~SELECT*FROM`student`WHERE`s_id`IN(SELECTDISTINCT`s_id`FROM`score`WHERE`s_id`!='01'AND`c_id`IN(SELECT`c_id`FROM`score`WHERE`s_id`='01')GROUPBY`s_id`HAVINGCOUNT(1)=(SELECTCOUNT(1)FROM`score`WHERE`s_id`='01'));-- 14、查询没学过"张三"老师讲授的任一门课程的学生姓名。SELECT 
  82.     st.`s_name`FROM`student` st
  83. WHERE
  84.     st.`s_id`NOTIN(SELECT`s_id`FROM`score`WHERE`c_id`=(SELECT`c_id`FROM`course`WHERE`t_id`=(SELECT`t_id`FROM`teacher`WHERE`t_name`='老师 1'))GROUPBY s_id);-- 15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩。SELECT 
  85.     st.`s_id`, st.`s_name`,AVG(sc.`s_score`) avg_score
  86. FROM`student` st
  87.         LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGSUM(IF(sc.`s_score`>=60,0,1))>=2;SELECT 
  88.     st.`s_id`, st.`s_name`,AVG(sc.`s_score`) avg_score
  89. FROM`student` st
  90.         LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`GROUPBY st.`s_id`HAVINGSUM(IF(sc.`s_score`>=60,0,1))>=2;SELECT 
  91.     st.`s_id`, st.`s_name`,ROUND(AVG(sc.`s_score`))FROM
  92.     student st
  93.         LEFTJOIN
  94.     score sc ON st.`s_id`= sc.`s_id`WHERE
  95.     st.`s_id`IN(SELECT`s_id`FROM`score`WHERE`s_score`<60GROUPBY`s_id`HAVINGCOUNT(1)>=2)GROUPBY st.`s_id`, st.`s_name`;-- 16、检索课程"01"分数小于 60，按分数降序排列的学生信息。SELECT 
  96.     st.*, sc.`s_score`FROM`score` sc
  97.         RIGHTJOIN`student` st ON sc.`s_id`= st.`s_id`WHERE
  98.     sc.`c_id`='01'AND sc.`s_score`<60ORDERBY`s_score`DESC;SELECT 
  99.     st.*, sc.`c_id`, sc.`s_score`FROM`student` st,`score` sc
  100. WHERE
  101.     st.`s_id`= sc.`s_id`AND sc.`c_id`='01'AND sc.`s_score`<60ORDERBY sc.`s_score`DESC;-- 17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩。SELECT sc.`s_id`,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='01')AS 语文,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='02')AS 数学,(SELECT`s_score`FROM`score`WHERE`s_id`= sc.`s_id`AND`c_id`='03')AS 英语,ROUND(AVG(`s_score`),2)AS 平均分
  102. FROM`score` sc
  103. GROUPBY sc.`s_id`ORDERBY 平均分 DESC;-- 18.查询各科成绩最高分、最低分和平均分，以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率。-- 及格为 >= 60，中等为：70 ~ 80，优良为：80 ~ 90，优秀为：>= 90。SELECT sc.`c_id`,
  104.        c.`c_name`,MAX(`s_score`),MIN(`s_score`),ROUND(AVG(`s_score`),2),ROUND(100*(SUM(IF(sc.`s_score`>=60,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 及格率,ROUND(100*(SUM(IF(sc.`s_score`>=70AND sc.`s_score`<=80,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 中等率,ROUND(100*(SUM(IF(sc.`s_score`>=80AND sc.`s_score`<=90,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 优良率,ROUND(100*(SUM(IF(sc.`s_score`>=90,1,0))/SUM(IF(sc.`s_score`,1,0))),2)AS 优秀率
  105. FROM`score` sc
  106.          LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`GROUPBY sc.`c_id`, c.`c_name`;-- 19、按各科成绩进行排序，并显示排名（实现不完全）。-- mysql 没有 rank(); 函数。SELECT 
  107.     sc1.`c_id`,
  108.     sc1.`s_id`,
  109.     sc1.`s_score`,COUNT(sc2.`s_score`)+1AS`rank`FROM`score` sc1
  110.         LEFTJOIN`score` sc2 ON sc1.`s_score`< sc2.`s_score`AND sc1.`c_id`= sc2.`c_id`GROUPBY sc1.`c_id`, sc1.`s_id`, sc1.`s_score`ORDERBY sc1.`c_id`,`rank`;-- 20、查询学生的总成绩并进行排名。SELECT 
  111.     t1.`s_id`,@i:=@i+1AS i,@k:=(IF(@score= t1.sum_score,@k,@i))AS`rank`,@score:=t1.sum_score AS score
  112. FROM(SELECT`s_id`,SUM(`s_score`)AS sum_score
  113.     FROM`score`GROUPBY`s_id`ORDERBY sum_score DESC) t1,(SELECT@k:=0,@i:=0,@score:=0)AS kis;-- 21、查询不同老师所教不同课程平均分从高到低显示。SELECT 
  114.     c.`t_id`,
  115.     t.`t_name`,
  116.     c.`c_id`,ROUND(AVG(`s_score`),2)AS avg_score
  117. FROM`course` c
  118.         LEFTJOIN`score` sc ON c.`c_id`= sc.`c_id`LEFTJOIN`teacher` t ON c.`t_id`= t.`t_id`GROUPBY c.`c_id`, c.`t_id`, t.`t_name`ORDERBY avg_score DESC;-- 22、查询所有课程的成绩第 2 名到第 3 名的学生信息及该课程成绩。SELECT d.*,
  119.        si2.排名,
  120.        si2.`s_score`,
  121.        si2.`c_id`FROM(SELECT sc.`s_id`,
  122.              sc.`s_score`,
  123.              sc.`c_id`,@i :=@i+1AS 排名
  124.       FROM`score` sc,(SELECT@i :=0)as i2
  125.       WHERE sc.c_id ='01')as si2
  126.          LEFTJOIN
  127.      student d ON si2.s_id = d.s_id
  128. WHERE 排名 BETWEEN2AND3UNIONSELECT st.*,
  129.        sj2.排名,
  130.        sj2.s_score,
  131.        sj2.c_id
  132. FROM(SELECT sc.s_id,
  133.              sc.s_score,
  134.              sc.c_id,@j :=@j+1AS 排名
  135.       FROM`score` sc,(SELECT@j :=0)as j2
  136.       WHERE sc.c_id ='02')as sj2
  137.          LEFTJOIN`student` st ON sj2.s_id = st.s_id
  138. WHERE 排名 BETWEEN2AND3UNIONSELECT d.*,
  139.        s.排名,
  140.        s.`s_score`,
  141.        s.`c_id`FROM(SELECT sc.`s_id`,
  142.              sc.`s_score`,
  143.              sc.`c_id`,@k :=@k+1AS 排名
  144.       FROM`score` sc,(SELECT@k :=0)as k2
  145.       WHERE sc.`c_id`='03')as s
  146.          LEFTJOIN`student` d ON s.`s_id`= d.`s_id`WHERE 排名 BETWEEN2AND3;-- 23、统计各科成绩各分数段人数：课程编号, 课程名称, [100-85], [85-70], [70-60], [0-60] 及所占百分比。SELECTDISTINCT c.`c_name`,
  147.                 sc.`c_id`,
  148.                 t1.`85-100`,
  149.                 t1.百分比,
  150.                 t2.`70-85`,
  151.                 t2.百分比,
  152.                 t3.`60-70`,
  153.                 t3.百分比,
  154.                 t4.`0-60`,
  155.                 t4.百分比
  156. FROM`score` sc
  157.          LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>85AND`s_score`<=100,1,0))AS`85-100`,ROUND(100*(SUM(IF(`s_score`>85AND`s_score`<=100,1,0))/COUNT(*)),2)AS 百分比
  158.       FROM`score`GROUPBY`c_id`) t1 ON sc.`c_id`= t1.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>70AND`s_score`<=85,1,0))AS`70-85`,ROUND(100*(SUM(IF(`s_score`>70AND`s_score`<=85,1,0))/COUNT(*)),2)AS 百分比
  159.       FROM`score`GROUPBY`c_id`) t2 ON sc.`c_id`= t2.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>60AND`s_score`<=70,1,0))AS`60-70`,ROUND(100*(SUM(IF(`s_score`>60AND`s_score`<=70,1,0))/COUNT(*)),2)AS 百分比
  160.       FROM`score`GROUPBY`c_id`) t3 ON sc.`c_id`= t3.`c_id`LEFTJOIN(SELECT`c_id`,SUM(IF(`s_score`>=0AND`s_score`<=60,1,0))AS`0-60`,ROUND(100*(SUM(IF(`s_score`>=0AND`s_score`<=60,1,0))/COUNT(*)),2)AS 百分比
  161.       FROM`score`GROUPBY`c_id`) t4 ON sc.`c_id`= t4.`c_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`;-- 24、查询学生平均成绩及其名次。SELECT t.`s_id`,@i :=@i+1AS'不保留空缺排名',@k :=(IF(@avg_score= t.avg_score,@k,@i))AS'保留空缺排名',@avg_score := avg_score                      AS'平均分'FROM(SELECT`s_id`,ROUND(AVG(`s_score`),2)AS avg_score
  162.       FROM score
  163.       GROUPBY`s_id`) t,(SELECT@avg_score :=0,@i :=0,@k :=0) b;-- 25、查询各科成绩前三名的记录。-- - 选出 sc1 表比 sc2 表成绩大的所有组。-- - 选出比当前 id 成绩大的小于三个的。SELECT 
  164.     sc1.`s_id`, sc1.`c_id`, sc1.`s_score`FROM`score` sc1
  165.         LEFTJOIN`score` sc2 ON sc1.`c_id`= sc2.`c_id`AND sc1.`s_score`< sc2.`s_score`GROUPBY sc1.`s_id`, sc1.`c_id`, sc1.`s_score`HAVINGCOUNT(sc2.`s_id`)<3ORDERBY sc1.`c_id`, sc1.`s_score`DESC;-- 26、查询每门课程被选修的学生数。SELECT`c_id`,COUNT(`s_id`)FROM`score`GROUPBY`c_id`;-- 27、查询出只有两门课程的全部学生的学号和姓名。SELECT`s_id`,`s_name`FROM`student`WHERE`s_id`IN(SELECT`s_id`FROM`score`GROUPBY`s_id`HAVINGCOUNT(`c_id`)=2);-- 28、查询男生、女生人数。SELECT`s_sex`,COUNT(`s_sex`)AS 人数
  166. FROM
  167.     student
  168. GROUPBY s_sex;-- 29、查询名字中含有"风"字的学生信息。SELECT*FROM`student`WHERE`s_name`LIKE'%风%';-- 30、查询同名同性学生名单，并统计同名人数。SELECT 
  169.     st1.`s_name`, st1.`s_sex`,COUNT(*)FROM`student` st1
  170.         JOIN`student` st2 ON st1.`s_id`!= st2.`s_id`AND st1.`s_name`= st2.`s_name`AND st1.`s_sex`= st2.`s_sex`GROUPBY st1.`s_name`, st1.`s_sex`;-- 31、查询 1990 年出生的学生名单。SELECT`s_name`FROM`student`WHERE`s_birth`LIKE'1990%';-- 32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列。SELECT`c_id`,ROUND(AVG(`s_score`),2)AS avg_score
  171. FROM`score`GROUPBY`c_id`ORDERBY avg_score DESC,`c_id`ASC;-- 33、查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩。SELECT 
  172.     sc.`s_id`,
  173.     st.`s_name`,ROUND(AVG(sc.`s_score`),2)AS avg_score
  174. FROM`score` sc
  175.         LEFTJOIN`student` st ON sc.`s_id`= st.`s_id`GROUPBY`s_id`HAVING avg_score >=85;-- 34、查询课程名称为"数学"，且分数低于 60 的学生姓名和分数。SELECT 
  176.     st.`s_name`, sc.`s_score`FROM`score` sc
  177.         LEFTJOIN`student` st ON st.`s_id`= sc.`s_id`WHERE
  178.     sc.`c_id`=(SELECT`c_id`FROM`course`WHERE`c_name`='数学')AND sc.s_score <60;-- 35、查询所有学生的课程及分数情况。SELECT st.`s_id`,
  179.        st.`s_name`,SUM(IF(c.`c_name`='语文', sc.`s_score`,0))AS'语文',SUM(IF(c.`c_name`='数学', sc.`s_score`,0))AS'数学',SUM(IF(c.`c_name`='英语', sc.`s_score`,0))AS'英语',SUM(sc.`s_score`)AS'总分'FROM`student` st
  180.          LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`GROUPBY st.`s_id`, st.`s_name`;-- 36、查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数。SELECT 
  181.     st.`s_name`, c.`c_name`, sc.`s_score`FROM`course` c
  182.         LEFTJOIN`score` sc ON c.`c_id`= sc.`c_id`LEFTJOIN`student` st ON st.`s_id`= sc.`s_id`WHERE
  183.     sc.`s_score`>=70;-- 37、查询不及格的课程。SELECT 
  184.     sc.`s_id`, sc.`c_id`, c.`c_name`, sc.`s_score`FROM`score` sc
  185.         LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`WHERE
  186.     sc.`s_score`<60;-- 38、查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名。SELECT 
  187.     sc.`s_id`, st.`s_name`FROM`score` sc
  188.         LEFTJOIN`student` st ON sc.`s_id`= st.`s_id`WHERE
  189.     sc.`c_id`='01'AND sc.`s_score`>80;-- 39、求每门课程的学生人数。SELECTCOUNT(*)FROM`score`GROUPBY`c_id`;-- 40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩。-- 查询老师 id。SELECT`c_id`FROM`course` c,`teacher` t
  190. WHERE
  191.     c.`t_id`= t.`t_id`AND t.`t_name`='老师 1';-- 查询最高分（可能有相同分数）。SELECTMAX(`s_score`)FROM`score`WHERE`c_id`='02';-- 查询信息。SELECT 
  192.     st.*, sc.`s_score`, sc.`c_id`, c.`c_name`FROM`student` st
  193.         LEFTJOIN`score` sc ON st.`s_id`= sc.`s_id`LEFTJOIN`course` c ON sc.`c_id`= c.`c_id`WHERE
  194.     sc.`c_id`=(SELECT`c_id`FROM`course` c,`teacher` t
  195.         WHERE
  196.             c.`t_id`= t.`t_id`AND t.`t_name`='老师 1')AND sc.s_score IN(SELECTMAX(s_score)FROM
  197.             score
  198.         WHERE
  199.             c_id ='02');SELECT 
  200.     c.`c_name`, sc.`s_score`, st.*FROM`course` c,`score` sc,`teacher` t,`student` st
  201. WHERE
  202.     t.`t_id`= c.`t_id`AND c.`c_id`= sc.`c_id`AND st.`s_id`= sc.`s_id`AND t.`t_name`='老师 1'AND sc.s_score IN(SELECTMAX(s_score)FROM
  203.             course,
  204.             score,
  205.             teacher,
  206.             student
  207.         WHERE
  208.             teacher.t_id = course.t_id
  209.                 AND course.c_id = score.c_id
  210.                 AND student.s_id = score.s_id
  211.                 AND teacher.t_name ='老师 1');-- 41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩。SELECTDISTINCT
  212.     sc2.`s_id`, sc2.`c_id`, sc2.`s_score`FROM`score` sc1,`score` sc2
  213. WHERE
  214.     sc1.`c_id`!= sc2.`c_id`AND sc1.`s_score`= sc2.`s_score`;-- 42、查询每门功成绩最好的前两名。-- 牛逼的写法。SELECT 
  215.     sc1.`s_id`, sc1.`c_id`, sc1.`s_score`FROM`score` sc1
  216. WHERE(SELECTCOUNT(1)FROM`score` sc2
  217.         WHERE
  218.             sc2.`c_id`= sc1.`c_id`AND sc2.`s_score`>= sc1.`s_score`)<=2ORDERBY sc1.`c_id`;-- 43、统计每门课程的学生选修人数（超过 5 人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列。SELECT`c_id`,COUNT(*)AS total
  219. FROM`score`GROUPBY`c_id`HAVING total >5ORDERBY total DESC,`c_id`;-- 44、检索至少选修两门课程的学生学号。SELECT`s_id`,COUNT(*)FROM`score`GROUPBY`s_id`HAVINGCOUNT(*)>=2;-- 45、查询选修了全部课程的学生信息。SELECT*FROM`student`WHERE`s_id`IN(SELECT`s_id`FROM`score`GROUPBY`s_id`HAVINGCOUNT(*)=(SELECTCOUNT(*)FROM`course`));-- 46、查询各学生的年龄。-- 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一。SELECT`s_birth`,(DATE_FORMAT(NOW(),'%Y')- DATE_FORMAT(`s_birth`,'%Y')-(IF(DATE_FORMAT(NOW(),'%m%d')> DATE_FORMAT(`s_birth`,'%m%d'),0,1)))AS age
  220. FROM`student`;-- 47、查询本周过生日的学生。SELECT*FROM`student`WHERE
  221.     WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))= WEEK(`s_birth`);SELECT*FROM`student`WHERE
  222.     YEARWEEK(`s_birth`)= YEARWEEK(DATE_FORMAT(NOW(),'%Y%m%d'));SELECT WEEK(DATE_FORMAT(NOW(),'%Y%m%d'));-- 48、查询下周过生日的学生。SELECT*FROM`student`WHERE
  223.     WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1= WEEK(`s_birth`);-- 49、查询本月过生日的学生。SELECT*FROM`student`WHEREMONTH(DATE_FORMAT(NOW(),'%Y%m%d'))=MONTH(`s_birth`);-- 50、查询下月过生日的学生。SELECT*FROM`student`WHEREMONTH(DATE_FORMAT(NOW(),'%Y-%m-%d'))+1=MONTH(`s_birth`);
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MySQL 50 题。