MySQL 50 题。

MySQL 50 题。

文章目录

    • MySQL 50 题。
      • 数据库。
      • sql。

数据库。

CREATE SCHEMA `new_schema` DEFAULT CHARACTER SET utf8mb4 ;Operation failed: There was an error while applying the SQL script to the database.
Executing:
CREATE SCHEMA `new_schema` DEFAULT CHARACTER SET utf8mb4 ;ERROR 1044: Access denied for user 'lyfgeek'@'%' to database 'new_schema'
SQL Statement:
CREATE SCHEMA `new_schema` DEFAULT CHARACTER SET utf8mb4
CREATE SCHEMA `mysql_fifty` DEFAULT CHARACTER SET utf8 ;
CREATE TABLE `lyfgeek`.`student`
(`id`             BIGINT      NOT NULL AUTO_INCREMENT COMMENT '主键 id。',`s_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '学生 id。',`s_name`         VARCHAR(45) NOT NULL DEFAULT '' COMMENT '姓名。',`s_birth`        VARCHAR(45) NOT NULL DEFAULT '' COMMENT '出生年月。',`s_sex`          VARCHAR(45) NOT NULL DEFAULT '' COMMENT '性别。',`db_insert_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'db_insert_time。',`db_update_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT 'db_update_time。',`db_deleted`     INT         NOT NULL DEFAULT 0 COMMENT 'db_deleted。',PRIMARY KEY (`id`, `s_id`),UNIQUE INDEX `s_id_UNIQUE` (`s_id` ASC) VISIBLE
)ENGINE = InnoDBDEFAULT CHARACTER SET = utf8mb4COMMENT = '学生。';-- 课程表。
CREATE TABLE `lyfgeek`.`course`
(`id`             BIGINT      NOT NULL AUTO_INCREMENT COMMENT '主键 id。',`c_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '课程 id。',`c_name`         VARCHAR(45) NOT NULL DEFAULT '' COMMENT '课程名称。',`t_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '教师 id。',`db_insert_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'db_insert_time。',`db_update_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT 'db_update_time。',`db_deleted`     INT         NOT NULL DEFAULT 0 COMMENT 'db_deleted。',PRIMARY KEY (`id`),UNIQUE INDEX `c_id_UNIQUE` (`c_id` ASC) VISIBLE
)ENGINE = InnoDBDEFAULT CHARACTER SET = utf8mb4COMMENT = '成绩。';-- 教师表。
CREATE TABLE `lyfgeek`.`teacher`
(`id`             BIGINT      NOT NULL AUTO_INCREMENT COMMENT '主键 id。',`t_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '教师 id。',`t_name`         VARCHAR(45) NOT NULL DEFAULT '' COMMENT '姓名。',`db_insert_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'db_insert_time。',`db_update_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT 'db_update_time。',`db_deleted`     INT         NOT NULL DEFAULT 0 COMMENT 'db_deleted。',PRIMARY KEY (`id`, `t_id`),UNIQUE INDEX `t_id_UNIQUE` (`t_id` ASC) VISIBLE
)ENGINE = InnoDBDEFAULT CHARACTER SET = utf8mb4COMMENT = '教师。';-- 成绩表。
CREATE TABLE `lyfgeek`.`score`
(`id`             BIGINT      NOT NULL AUTO_INCREMENT COMMENT '主键 id。',`s_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '学生 id。',`c_id`           VARCHAR(45) NOT NULL DEFAULT '' COMMENT '课程 id。',`s_score`        INT         NULL     DEFAULT NULL COMMENT '成绩。',`db_insert_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'db_insert_time。',`db_update_time` TIMESTAMP   NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT 'db_update_time。',`db_deleted`     INT         NOT NULL DEFAULT 0 COMMENT 'db_deleted。',PRIMARY KEY (`id`)
)ENGINE = InnoDBDEFAULT CHARACTER SET = utf8mb4COMMENT = '成绩。';# 学生表测试数据。
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('01', '学生 1', '2021-01-01', '男');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('02', '学生 2', '2022-02-02', '男');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('03', '学生 3', '2023-03-03', '男');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('04', '学生 4', '2024-04-04', '男');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('05', '学生 5', '2025-05-05', '女');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('06', '学生 6', '2026-06-06', '女');
INSERT INTO `lyfgeek`.`student` (`s_id`, `s_name`, `s_birth`, `s_sex`)
VALUES ('07', '学生 7', '2027-07-07', '女');
INSERT INTO `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。
INSERT INTO `lyfgeek`.`course`(`c_id`, `c_name`, `t_id`)
VALUES ('01', '语文', '02');
INSERT INTO `lyfgeek`.`course`(`c_id`, `c_name`, `t_id`)
VALUES ('02', '数学', '01');
INSERT INTO `lyfgeek`.`course`(`c_id`, `c_name`, `t_id`)
VALUES ('03', '英语', '03');# 教师表测试数据。
INSERT INTO `lyfgeek`.`teacher` (`t_id`, `t_name`)
VALUES ('01', '老师 1');
INSERT INTO `lyfgeek`.`teacher` (`t_id`, `t_name`)
VALUES ('02', '老师 2');
INSERT INTO `lyfgeek`.`teacher` (`t_id`, `t_name`)
VALUES ('03', '老师 3');# 成绩表测试数据。
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('01', '01', '80');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('01', '02', '90');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('01', '03', '99');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('02', '01', '70');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('02', '02', '60');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('02', '03', '80');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('03', '01', '80');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('03', '02', '80');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('03', '03', '80');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('04', '01', '50');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('04', '02', '30');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('04', '03', '20');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('05', '01', '76');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('05', '02', '87');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('06', '01', '31');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('06', '03', '34');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('07', '02', '89');
INSERT INTO `lyfgeek`.`score` (`s_id`, `c_id`, `s_score`)
VALUES ('07', '03', '98');

sql。

-- 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.*,t.s01,t.s02
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) s02FROM `score` scGROUP BY sc.`s_id`) t,`student` st
WHERE t.s01 > t.s02AND t.`s_id` = st.`s_id`;-- 自连接。
SELECT st.*,sc1.`s_score`,sc2.`s_score`
FROM `student` st,`score` sc1,`score` sc2
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`.*,sc1.`s_score`,sc2.`s_score`
FROM `student`INNER JOIN`score` sc1 ON `student`.`s_id` = sc1.`s_id`AND sc1.`c_id` = '01'INNER JOIN`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` IS NULL;-- 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` stWHERE st.`s_id` = sc.`s_id`) AS s_name,AVG(sc.`s_score`)                avg_score
FROM `score` sc
GROUP BY sc.`s_id`
HAVING avg_score >= 60;-- 两个表连接方法。
SELECT st.`s_id`,st.`s_name`,AVG(sc.`s_score`)
FROM `student` st,`score` sc
WHERE st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING AVG(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`,st.`s_name`,AVG(sc.`s_score`) AS avg_score
FROM `student` st,`score` sc
WHERE st.`s_id` = sc.`s_id`
GROUP BY sc.`s_id`
HAVING AVG(sc.`s_score`) < 60
UNION
SELECT st.`s_id`,st.`s_name`,0 AS avg_score
FROM `student` st
WHERE st.`s_id` NOT IN (SELECT DISTINCT `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`,st.`s_name`,COUNT(sc.s_id)               AS sum_course,IFNULL(SUM(sc.`s_score`), 0) AS sum_score
FROM `student` stLEFT OUTER JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`;-- 6、查询"李"姓老师的数量。
SELECT COUNT(`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` stJOIN`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` stINNER JOIN`score` sc ON st.`s_id` = sc.`s_id`
WHERE sc.`c_id` IN (SELECT `c_id`FROM `course` cINNER JOIN`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
WHERE st.s_id NOT IN (SELECT st.`s_id`FROM `student` stJOIN`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` NOT IN (SELECT sc.`s_id`FROM `teacher` t,`score` sc,`course` cWHERE t.`t_id` = c.`t_id`AND c.`c_id` = sc.`c_id`AND t.`t_name` = '老师 1');SELECT *
FROM `student`
WHERE NOT EXISTS(SELECT 1FROM (SELECT sc.`s_id`FROM `teacher` t,`score` sc,`course` cWHERE t.`t_id` = c.`t_id`AND c.`c_id` = sc.`c_id`AND t.`t_name` = '老师 1') tWHERE 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
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
WHERE st.`s_id` IN (SELECT `s_id`FROM `score`WHERE `c_id` = '01')AND st.`s_id` NOT IN (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)) s02FROM `score`GROUP BY `s_id`) t
WHERE t.`s_id` = st.`s_id`AND t.s01 IS NOT NULLAND t.s02 IS NULL;-- 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
FROM `student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING COUNT(sc.`c_id`) < (SELECT COUNT(`c_id`)FROM `course`);SELECT st.*
FROM `student` st
WHERE st.`s_id` IN (SELECT `s_id`FROM `score`WHERE `s_id` NOT IN (SELECT sc1.`s_id`FROM `score` sc1JOIN`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 (SELECT DISTINCT `s_id`FROM `score`WHERE `c_id` IN (SELECT `c_id`FROM `score`WHERE `s_id` = '01'))
GROUP BY 1, 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。
CREATE TABLE s01_sc_temp AS
SELECT t1.*, sc.`c_id` cid2
FROM (SELECT st.*,t2.`c_id`FROM `student` st,(SELECT `c_id`FROM `score`WHERE `s_id` = '01') t2) t1LEFT JOIN`score` sc ON t1.`s_id` = sc.`s_id`AND t1.`c_id` = sc.`c_id`
UNION
SELECT t.*,sc.`c_id` cid2
FROM (SELECT st.*,b.`c_id`FROM `student` st,(SELECT `c_id`FROM `score`WHERE `s_id` = '01') b) tRIGHT JOIN`score` sc ON t.`s_id` = sc.`s_id`AND t.`c_id` = sc.`c_id`;SELECT *
FROM `student`
WHERE `s_id` NOT IN (SELECT `s_id`FROM s01_s_tempWHERE cid2 IS NULLOR `c_id` IS NULL)AND `s_id` != '01';-- ~ ~ ~SELECT *
FROM `student`
WHERE `s_id` IN (SELECT DISTINCT `s_id`FROM `score`WHERE `s_id` != '01'AND `c_id` IN (SELECT `c_id`FROM `score`WHERE `s_id` = '01')GROUP BY `s_id`HAVING COUNT(1) = (SELECT COUNT(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
WHERE st.`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` = '老师 1'))GROUP BY 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`,st.`s_name`,AVG(sc.`s_score`) avg_score
FROM `student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING SUM(IF(sc.`s_score` >= 60, 0, 1)) >= 2;SELECT st.`s_id`,st.`s_name`,AVG(sc.`s_score`) avg_score
FROM `student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING SUM(IF(sc.`s_score` >= 60, 0, 1)) >= 2;SELECT st.`s_id`,st.`s_name`,ROUND(AVG(sc.`s_score`))
FROM student stLEFT JOINscore sc ON st.`s_id` = sc.`s_id`
WHERE st.`s_id` IN (SELECT `s_id`FROM `score`WHERE `s_score` < 60GROUP BY `s_id`HAVING COUNT(1) >= 2)
GROUP BY 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.*,sc.`s_score`
FROM `score` scRIGHT JOIN`student` st ON sc.`s_id` = st.`s_id`
WHERE sc.`c_id` = '01'AND sc.`s_score` < 60
ORDER BY `s_score` DESC;SELECT st.*,sc.`c_id`,sc.`s_score`
FROM `student` st,`score` sc
WHERE st.`s_id` = sc.`s_id`AND sc.`c_id` = '01'AND sc.`s_score` < 60
ORDER BY 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
FROM `score` sc
GROUP BY sc.`s_id`
ORDER BY 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`,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` >= 70 AND 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` >= 80 AND 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
FROM `score` scLEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
GROUP BY 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`,sc1.`s_id`,sc1.`s_score`,COUNT(sc2.`s_score`) + 1 AS `rank`
FROM `score` sc1LEFT JOIN`score` sc2 ON sc1.`s_score` < sc2.`s_score`AND sc1.`c_id` = sc2.`c_id`
GROUP BY sc1.`c_id`, sc1.`s_id`, sc1.`s_score`
ORDER BY sc1.`c_id`, `rank`;-- 20、查询学生的总成绩并进行排名。
SELECT t1.`s_id`,@i := @i + 1                              AS i,@k := (IF(@score = t1.sum_score, @k, @i)) AS `rank`,@score := t1.sum_score                    AS score
FROM (SELECT `s_id`,SUM(`s_score`) AS sum_scoreFROM `score`GROUP BY `s_id`ORDER BY 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`,t.`t_name`,c.`c_id`,ROUND(AVG(`s_score`), 2) AS avg_score
FROM `course` cLEFT JOIN`score` sc ON c.`c_id` = sc.`c_id`LEFT JOIN`teacher` t ON c.`t_id` = t.`t_id`
GROUP BY c.`c_id`, c.`t_id`, t.`t_name`
ORDER BY 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.*,si2.排名,si2.`s_score`,si2.`c_id`
FROM (SELECT sc.`s_id`,sc.`s_score`,sc.`c_id`,@i := @i + 1 AS 排名FROM `score` sc,(SELECT @i := 0) as i2WHERE sc.c_id = '01') as si2LEFT JOINstudent d ON si2.s_id = d.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT st.*,sj2.排名,sj2.s_score,sj2.c_id
FROM (SELECT sc.s_id,sc.s_score,sc.c_id,@j := @j + 1 AS 排名FROM `score` sc,(SELECT @j := 0) as j2WHERE sc.c_id = '02') as sj2LEFT JOIN`student` st ON sj2.s_id = st.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT d.*,s.排名,s.`s_score`,s.`c_id`
FROM (SELECT sc.`s_id`,sc.`s_score`,sc.`c_id`,@k := @k + 1 AS 排名FROM `score` sc,(SELECT @k := 0) as k2WHERE sc.`c_id` = '03') as sLEFT JOIN`student` d ON s.`s_id` = d.`s_id`
WHERE 排名 BETWEEN 2 AND 3;-- 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。
SELECT DISTINCT c.`c_name`,sc.`c_id`,t1.`85-100`,t1.百分比,t2.`70-85`,t2.百分比,t3.`60-70`,t3.百分比,t4.`0-60`,t4.百分比
FROM `score` scLEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 85 AND `s_score` <= 100, 1, 0))                              AS `85-100`,ROUND(100 * (SUM(IF(`s_score` > 85 AND `s_score` <= 100, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t1 ON sc.`c_id` = t1.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 70 AND `s_score` <= 85, 1, 0))                              AS `70-85`,ROUND(100 * (SUM(IF(`s_score` > 70 AND `s_score` <= 85, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t2 ON sc.`c_id` = t2.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 60 AND `s_score` <= 70, 1, 0))                              AS `60-70`,ROUND(100 * (SUM(IF(`s_score` > 60 AND `s_score` <= 70, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t3 ON sc.`c_id` = t3.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` >= 0 AND `s_score` <= 60, 1, 0))                              AS `0-60`,ROUND(100 * (SUM(IF(`s_score` >= 0 AND `s_score` <= 60, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t4 ON sc.`c_id` = t4.`c_id`LEFT JOIN`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 + 1                                 AS '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_scoreFROM scoreGROUP BY `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`,sc1.`c_id`,sc1.`s_score`
FROM `score` sc1LEFT JOIN`score` sc2 ON sc1.`c_id` = sc2.`c_id`AND sc1.`s_score` < sc2.`s_score`
GROUP BY sc1.`s_id`, sc1.`c_id`, sc1.`s_score`
HAVING COUNT(sc2.`s_id`) < 3
ORDER BY 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`
GROUP BY `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`GROUP BY `s_id`HAVING COUNT(`c_id`) = 2);-- 28、查询男生、女生人数。
SELECT `s_sex`,COUNT(`s_sex`) AS 人数
FROM student
GROUP BY 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`,st1.`s_sex`,COUNT(*)
FROM `student` st1JOIN`student` st2 ON st1.`s_id` != st2.`s_id`AND st1.`s_name` = st2.`s_name`AND st1.`s_sex` = st2.`s_sex`
GROUP BY 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
FROM `score`
GROUP BY `c_id`
ORDER BY 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`,st.`s_name`,ROUND(AVG(sc.`s_score`), 2) AS avg_score
FROM `score` scLEFT JOIN`student` st ON sc.`s_id` = st.`s_id`
GROUP BY `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`,sc.`s_score`
FROM `score` scLEFT JOIN`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`,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` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`LEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
GROUP BY 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`,c.`c_name`,sc.`s_score`
FROM `course` cLEFT JOIN`score` sc ON c.`c_id` = sc.`c_id`LEFT JOIN`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`,sc.`c_id`,c.`c_name`,sc.`s_score`
FROM `score` scLEFT JOIN`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`,st.`s_name`
FROM `score` scLEFT JOIN`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。
SELECT COUNT(*)
FROM `score`
GROUP BY `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
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）。
SELECT MAX(`s_score`)
FROM `score`
WHERE `c_id` = '02';
-- 查询信息。
SELECT st.*,sc.`s_score`,sc.`c_id`,c.`c_name`
FROM `student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`LEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
WHERE sc.`c_id` = (SELECT `c_id`FROM `course` c,`teacher` tWHERE c.`t_id` = t.`t_id`AND t.`t_name` = '老师 1')AND sc.s_score IN (SELECT MAX(s_score)FROM scoreWHERE c_id = '02');SELECT c.`c_name`, sc.`s_score`, st.*
FROM `course` c,`score` sc,`teacher` t,`student` st
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 (SELECT MAX(`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。
SELECT DISTINCT sc2.`s_id`,sc2.`c_id`,sc2.`s_score`
FROM `score` sc1,`score` sc2
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`,sc1.`c_id`,sc1.`s_score`
FROM `score` sc1
WHERE (SELECT COUNT(1)FROM `score` sc2WHERE sc2.`c_id` = sc1.`c_id`AND sc2.`s_score` >= sc1.`s_score`) <= 2
ORDER BY 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
FROM `score`
GROUP BY `c_id`
HAVING total > 5
ORDER BY 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`
GROUP BY `s_id`
HAVING COUNT(*) >= 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`GROUP BY `s_id`HAVING COUNT(*) = (SELECT COUNT(*)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
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`
WHERE MONTH(DATE_FORMAT(NOW(), '%Y%m%d')) = MONTH(`s_birth`);-- 50、查询下月过生日的学生。
SELECT *
FROM `student`
WHERE MONTH(DATE_FORMAT(NOW(), '%Y-%m-%d')) + 1 = MONTH(`s_birth`);
-- 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.*, t.s01, t.s02
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) s02FROM`score` scGROUP BY sc.`s_id`) t,`student` st
WHEREt.s01 > t.s02 AND t.`s_id` = st.`s_id`;-- 自连接。
SELECT st.*, sc1.`s_score`, sc2.`s_score`
FROM`student` st,`score` sc1,`score` sc2
WHEREst.`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`INNER JOIN`score` sc1 ON `student`.`s_id` = sc1.`s_id`AND sc1.`c_id` = '01'INNER JOIN`score` sc2 ON sc1.`s_id` = sc2.`s_id`AND sc2.`c_id` = '02'
WHEREsc1.`s_score` < sc2.`s_score`OR sc1.`s_score` IS NULL;-- 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` stWHEREst.`s_id` = sc.`s_id`) AS s_name,AVG(sc.`s_score`) avg_score
FROM`score` sc
GROUP BY sc.`s_id`
HAVING avg_score >= 60;-- 两个表连接方法。
SELECT st.`s_id`, st.`s_name`, AVG(sc.`s_score`)
FROM`student` st,`score` sc
WHEREst.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING AVG(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`, st.`s_name`, AVG(sc.`s_score`) AS avg_score
FROM`student` st,`score` sc
WHEREst.`s_id` = sc.`s_id`
GROUP BY sc.`s_id`
HAVING AVG(sc.`s_score`) < 60 
UNION SELECT st.`s_id`, st.`s_name`, 0 AS avg_score
FROM`student` st
WHEREst.`s_id` NOT IN (SELECT DISTINCT`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`,st.`s_name`,COUNT(sc.s_id) AS sum_course,IFNULL(SUM(sc.`s_score`), 0) AS sum_score
FROM`student` stLEFT OUTER JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`;-- 6、查询"李"姓老师的数量。
SELECT COUNT(`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` stJOIN`score` sc ON st.`s_id` = sc.`s_id`
WHEREsc.`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` stINNER JOIN`score` sc ON st.`s_id` = sc.`s_id`
WHEREsc.`c_id` IN (SELECT `c_id`FROM`course` cINNER JOIN`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
WHEREst.s_id NOT IN (SELECT st.`s_id`FROM`student` stJOIN`score` sc ON st.`s_id` = sc.`s_id`WHEREsc.`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` NOT IN (SELECT sc.`s_id`FROM`teacher` t,`score` sc,`course` cWHEREt.`t_id` = c.`t_id`AND c.`c_id` = sc.`c_id`AND t.`t_name` = '老师 1');SELECT *
FROM`student`
WHERENOT EXISTS( SELECT 1FROM(SELECT sc.`s_id`FROM`teacher` t, `score` sc, `course` cWHEREt.`t_id` = c.`t_id`AND c.`c_id` = sc.`c_id`AND t.`t_name` = '老师 1') tWHEREt.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
WHEREst.`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
WHEREst.`s_id` IN (SELECT `s_id`FROM`score`WHERE`c_id` = '01')AND st.`s_id` NOT IN (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)) s02FROM`score`GROUP BY `s_id`) t
WHEREt.`s_id` = st.`s_id`AND t.s01 IS NOT NULLAND t.s02 IS NULL;-- 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
FROM`student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING COUNT(sc.`c_id`) < (SELECT COUNT(`c_id`)FROM`course`);SELECT st.*
FROM`student` st
WHEREst.`s_id` IN (SELECT `s_id`FROM`score`WHERE`s_id` NOT IN (SELECT sc1.`s_id`FROM`score` sc1JOIN`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'WHEREsc1.`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 (SELECT DISTINCT`s_id`FROM`score`WHERE`c_id` IN (SELECT `c_id`FROM`score`WHERE`s_id` = '01'))
GROUP BY 1 , 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。
CREATE TABLE s01_sc_temp AS SELECT t1.*, sc.`c_id` cid2 FROM(SELECT st.*, t2.`c_id`FROM`student` st, (SELECT `c_id`FROM`score`WHERE`s_id` = '01') t2) t1LEFT JOIN`score` sc ON t1.`s_id` = sc.`s_id`AND t1.`c_id` = sc.`c_id` 
UNION SELECT t.*, sc.`c_id` cid2
FROM(SELECT st.*, b.`c_id`FROM`student` st, (SELECT `c_id`FROM`score`WHERE`s_id` = '01') b) tRIGHT JOIN`score` sc ON t.`s_id` = sc.`s_id`AND t.`c_id` = sc.`c_id`;SELECT *
FROM`student`
WHERE`s_id` NOT IN (SELECT `s_id`FROMs01_s_tempWHEREcid2 IS NULL OR `c_id` IS NULL)AND `s_id` != '01';-- ~ ~ ~SELECT *
FROM`student`
WHERE`s_id` IN (SELECT DISTINCT`s_id`FROM`score`WHERE`s_id` != '01'AND `c_id` IN (SELECT `c_id`FROM`score`WHERE`s_id` = '01')GROUP BY `s_id`HAVING COUNT(1) = (SELECT COUNT(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
WHEREst.`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` = '老师 1'))GROUP BY 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`, st.`s_name`, AVG(sc.`s_score`) avg_score
FROM`student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING SUM(IF(sc.`s_score` >= 60, 0, 1)) >= 2;SELECT st.`s_id`, st.`s_name`, AVG(sc.`s_score`) avg_score
FROM`student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`
GROUP BY st.`s_id`
HAVING SUM(IF(sc.`s_score` >= 60, 0, 1)) >= 2;SELECT st.`s_id`, st.`s_name`, ROUND(AVG(sc.`s_score`))
FROMstudent stLEFT JOINscore sc ON st.`s_id` = sc.`s_id`
WHEREst.`s_id` IN (SELECT `s_id`FROM`score`WHERE`s_score` < 60GROUP BY `s_id`HAVING COUNT(1) >= 2)
GROUP BY 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.*, sc.`s_score`
FROM`score` scRIGHT JOIN`student` st ON sc.`s_id` = st.`s_id`
WHEREsc.`c_id` = '01' AND sc.`s_score` < 60
ORDER BY `s_score` DESC;SELECT st.*, sc.`c_id`, sc.`s_score`
FROM`student` st,`score` sc
WHEREst.`s_id` = sc.`s_id`AND sc.`c_id` = '01'AND sc.`s_score` < 60
ORDER BY 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
FROM `score` sc
GROUP BY sc.`s_id`
ORDER BY 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`,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` >= 70 AND 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` >= 80 AND 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
FROM `score` scLEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
GROUP BY 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`,sc1.`s_id`,sc1.`s_score`,COUNT(sc2.`s_score`) + 1 AS `rank`
FROM`score` sc1LEFT JOIN`score` sc2 ON sc1.`s_score` < sc2.`s_score`AND sc1.`c_id` = sc2.`c_id`
GROUP BY sc1.`c_id` , sc1.`s_id` , sc1.`s_score`
ORDER BY sc1.`c_id` , `rank`;-- 20、查询学生的总成绩并进行排名。
SELECT t1.`s_id`,@i:=@i + 1 AS i,@k:=(IF(@score = t1.sum_score, @k, @i)) AS `rank`,@score:=t1.sum_score AS score
FROM(SELECT `s_id`, SUM(`s_score`) AS sum_scoreFROM`score`GROUP BY `s_id`ORDER BY 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`,t.`t_name`,c.`c_id`,ROUND(AVG(`s_score`), 2) AS avg_score
FROM`course` cLEFT JOIN`score` sc ON c.`c_id` = sc.`c_id`LEFT JOIN`teacher` t ON c.`t_id` = t.`t_id`
GROUP BY c.`c_id` , c.`t_id` , t.`t_name`
ORDER BY 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.*,si2.排名,si2.`s_score`,si2.`c_id`
FROM (SELECT sc.`s_id`,sc.`s_score`,sc.`c_id`,@i := @i + 1 AS 排名FROM `score` sc,(SELECT @i := 0) as i2WHERE sc.c_id = '01') as si2LEFT JOINstudent d ON si2.s_id = d.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT st.*,sj2.排名,sj2.s_score,sj2.c_id
FROM (SELECT sc.s_id,sc.s_score,sc.c_id,@j := @j + 1 AS 排名FROM `score` sc,(SELECT @j := 0) as j2WHERE sc.c_id = '02') as sj2LEFT JOIN`student` st ON sj2.s_id = st.s_id
WHERE 排名 BETWEEN 2 AND 3
UNION
SELECT d.*,s.排名,s.`s_score`,s.`c_id`
FROM (SELECT sc.`s_id`,sc.`s_score`,sc.`c_id`,@k := @k + 1 AS 排名FROM `score` sc,(SELECT @k := 0) as k2WHERE sc.`c_id` = '03') as sLEFT JOIN`student` d ON s.`s_id` = d.`s_id`
WHERE 排名 BETWEEN 2 AND 3;-- 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。
SELECT DISTINCT c.`c_name`,sc.`c_id`,t1.`85-100`,t1.百分比,t2.`70-85`,t2.百分比,t3.`60-70`,t3.百分比,t4.`0-60`,t4.百分比
FROM `score` scLEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 85 AND `s_score` <= 100, 1, 0))                              AS `85-100`,ROUND(100 * (SUM(IF(`s_score` > 85 AND `s_score` <= 100, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t1 ON sc.`c_id` = t1.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 70 AND `s_score` <= 85, 1, 0))                              AS `70-85`,ROUND(100 * (SUM(IF(`s_score` > 70 AND `s_score` <= 85, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t2 ON sc.`c_id` = t2.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` > 60 AND `s_score` <= 70, 1, 0))                              AS `60-70`,ROUND(100 * (SUM(IF(`s_score` > 60 AND `s_score` <= 70, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t3 ON sc.`c_id` = t3.`c_id`LEFT JOIN(SELECT `c_id`,SUM(IF(`s_score` >= 0 AND `s_score` <= 60, 1, 0))                              AS `0-60`,ROUND(100 * (SUM(IF(`s_score` >= 0 AND `s_score` <= 60, 1, 0)) / COUNT(*)), 2) AS 百分比FROM `score`GROUP BY `c_id`) t4 ON sc.`c_id` = t4.`c_id`LEFT JOIN`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 + 1                                 AS '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_scoreFROM scoreGROUP BY `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`, sc1.`c_id`, sc1.`s_score`
FROM`score` sc1LEFT JOIN`score` sc2 ON sc1.`c_id` = sc2.`c_id`AND sc1.`s_score` < sc2.`s_score`
GROUP BY sc1.`s_id` , sc1.`c_id` , sc1.`s_score`
HAVING COUNT(sc2.`s_id`) < 3
ORDER BY 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`
GROUP BY `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`GROUP BY `s_id`HAVING COUNT(`c_id`) = 2);-- 28、查询男生、女生人数。
SELECT `s_sex`, COUNT(`s_sex`) AS 人数
FROMstudent
GROUP BY 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`, st1.`s_sex`, COUNT(*)
FROM`student` st1JOIN`student` st2 ON st1.`s_id` != st2.`s_id`AND st1.`s_name` = st2.`s_name`AND st1.`s_sex` = st2.`s_sex`
GROUP BY 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
FROM`score`
GROUP BY `c_id`
ORDER BY 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`,st.`s_name`,ROUND(AVG(sc.`s_score`), 2) AS avg_score
FROM`score` scLEFT JOIN`student` st ON sc.`s_id` = st.`s_id`
GROUP BY `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`, sc.`s_score`
FROM`score` scLEFT JOIN`student` st ON st.`s_id` = sc.`s_id`
WHEREsc.`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`,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` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`LEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
GROUP BY 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`, c.`c_name`, sc.`s_score`
FROM`course` cLEFT JOIN`score` sc ON c.`c_id` = sc.`c_id`LEFT JOIN`student` st ON st.`s_id` = sc.`s_id`
WHEREsc.`s_score` >= 70;-- 37、查询不及格的课程。
SELECT sc.`s_id`, sc.`c_id`, c.`c_name`, sc.`s_score`
FROM`score` scLEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
WHEREsc.`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`, st.`s_name`
FROM`score` scLEFT JOIN`student` st ON sc.`s_id` = st.`s_id`
WHEREsc.`c_id` = '01' AND sc.`s_score` > 80;-- 39、求每门课程的学生人数。
SELECT COUNT(*)
FROM`score`
GROUP BY `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
WHEREc.`t_id` = t.`t_id`AND t.`t_name` = '老师 1';
-- 查询最高分（可能有相同分数）。
SELECT MAX(`s_score`)
FROM`score`
WHERE`c_id` = '02';
-- 查询信息。
SELECT st.*, sc.`s_score`, sc.`c_id`, c.`c_name`
FROM`student` stLEFT JOIN`score` sc ON st.`s_id` = sc.`s_id`LEFT JOIN`course` c ON sc.`c_id` = c.`c_id`
WHEREsc.`c_id` = (SELECT `c_id`FROM`course` c,`teacher` tWHEREc.`t_id` = t.`t_id`AND t.`t_name` = '老师 1')AND sc.s_score IN (SELECT MAX(s_score)FROMscoreWHEREc_id = '02');SELECT c.`c_name`, sc.`s_score`, st.*
FROM`course` c,`score` sc,`teacher` t,`student` st
WHEREt.`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 (SELECT MAX(s_score)FROMcourse,score,teacher,studentWHEREteacher.t_id = course.t_idAND course.c_id = score.c_idAND student.s_id = score.s_idAND 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。
SELECT DISTINCTsc2.`s_id`, sc2.`c_id`, sc2.`s_score`
FROM`score` sc1,`score` sc2
WHEREsc1.`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`, sc1.`c_id`, sc1.`s_score`
FROM`score` sc1
WHERE(SELECT COUNT(1)FROM`score` sc2WHEREsc2.`c_id` = sc1.`c_id`AND sc2.`s_score` >= sc1.`s_score`) <= 2
ORDER BY 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
FROM`score`
GROUP BY `c_id`
HAVING total > 5
ORDER BY 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`
GROUP BY `s_id`
HAVING COUNT(*) >= 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`GROUP BY `s_id`HAVING COUNT(*) = (SELECT COUNT(*)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
FROM`student`;-- 47、查询本周过生日的学生。
SELECT *
FROM`student`
WHEREWEEK(DATE_FORMAT(NOW(), '%Y%m%d')) = WEEK(`s_birth`);SELECT *
FROM`student`
WHEREYEARWEEK(`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`
WHEREWEEK(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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