《数据库》基础题一：两表相关查询

题目

系统初始了以下脚本数据向student表插入记录的INSERT语句如下：INSERT  INTO t_student  VALUES( 901,'张老大','男',1985,'计算机系','北京市海淀区'); INSERT  INTO t_student  VALUES( 902,'张老二','男',1986,'中文系','北京市昌平区'); INSERT  INTO t_student  VALUES( 903,'张三','女',1990,'中文系','湖南省永州市'); INSERT  INTO t_student  VALUES( 904,'李四','男',1990,'英语系','辽宁省阜新市'); INSERT  INTO t_student  VALUES( 905,'王五','女',1991,'英语系','福建省厦门市'); INSERT  INTO t_student  VALUES( 906,'王六','男',1988,'计算机系','湖南省衡阳市');向score表插入记录的INSERT语句如下：INSERT  INTO    t-score VALUES(NULL,901,'计算机',98);INSERT  INTO    t-score VALUES(NULL,901,'英语',80);INSERT  INTO    t-score VALUES(NULL,902,'中文',88); INSERT  INTO    t-score VALUES(NULL,904,'计算机',70); INSERT  INTO    t-score VALUES(NULL,904,'英语',92);INSERT  INTO    t-score VALUES(NULL,905,'英语',94); INSERT  INTO    t-score VALUES(NULL,906,'英语',85);

题目及相关代码

-- 创建student和score表语句 DROP TABLE IF EXISTS t_student;CREATE TABLE t_student(    id INT(10) AUTO_INCREMENT PRIMARY KEY,    name VARCHAR(200) NOT NULL,    sex VARCHAR(4),     birth YEAR,    department varchar(20) NOT NULL,    address VARCHAR(50));DROP TABLE IF EXISTS t_score;CREATE TABLE t_score(    id INT(10) AUTO_INCREMENT PRIMARY KEY,    stu_id INT(10) NOT NULL,    c_name VARCHAR(20),    grade INT(10));-- 向student表插入记录的insert语句如下：INSERT INTO t_student VALUES(901,'张老大','男',1985,'计算机系','北京市海淀区');INSERT INTO t_student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');INSERT INTO t_student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');INSERT INTO t_student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');INSERT INTO t_student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');INSERT INTO t_student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');-- 向score表插入记录的INSERT语句如下：INSERT INTO t_score VALUES(NULL,901, '计算机',98);INSERT INTO t_score VALUES(NULL,901, '英语', 80);INSERT INTO t_score VALUES(NULL,902, '计算机',65);INSERT INTO t_score VALUES(NULL,902, '中文',88);INSERT INTO t_score VALUES(NULL,903, '中文',95);INSERT INTO t_score VALUES(NULL,904, '计算机',70);INSERT INTO t_score VALUES(NULL,904, '英语',92);INSERT INTO t_score VALUES(NULL,905, '英语',94);INSERT INTO t_score VALUES(NULL,906, '计算机',90);INSERT INTO t_score VALUES(NULL,906, '英语',85);-- 查询student表的所有记录 SELECT * FROM t_student;-- 查询student表的第2条到4条记录 SELECT * FROM t_student LIMIT 1,3;-- 从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息 SELECT id,name,department FROM t_student;-- 从student表中查询计算机系和英语系的学生的信息（用 IN 关键字）SELECT * FROM t_student WHERE department in ('计算机系','英语系'); -- 从student表中查询年龄18~22岁的学生信息（用 BETWEEN AND） SELECT * FROM t_student #WHERE (DATE_FORMAT(NOW(), '%Y') - birth)WHERE (YEAR(NOW()) - birth)BETWEEN 18 AND 42;-- 从student表中查询每个院系有多少人SELECT department,COUNT(*)FROM t_studentGROUP BY department;-- 从score表中查询每个科目的最高分 SELECT s.c_name,MAX(s.grade)FROM t_score AS sWHERE s.c_name IS NOT NULLGROUP BY s.c_name;-- 查询李四的考试科目（c_name）和考试成绩（grade） SELECT s.`name`,e.c_name,e.gradeFROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.idWHERE s.name = '李四';-- 用连接的方式查询所有学生的信息和考试信息 SELECT * FROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.id;-- 计算每个学生的总成绩 SELECT stu_id,SUM(grade)FROM t_scoreGROUP BY stu_id;-- 计算每个考试科目的平均成绩 SELECT c_name,AVG(grade)FROM t_scoreWHERE c_name IS NOT NULLGROUP BY c_name;-- 查询计算机成绩低于95的学生信息 SELECT*FROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.idWHERE e.c_name = '计算机'AND e.grade < 95;#方法二 考试科目没有唯一性约束（可能存在补考，即同一个学生补考了两次）SELECT * FROM t_studentWHERE id IN(SELECT stu_id FROM t_scoreWHERE c_name = '计算机' AND grade < 95);-- 查询同时参加计算机和英语考试的学生的信息SELECT * FROM t_student WHERE id = ANY(    SELECT stu_id FROM t_score     WHERE stu_id IN(SELECT stu_id FROM t_score WHERE c_name = '计算机') AND c_name = '英语'); #方法二：SELECT a.*FROM t_student a,t_score b, t_score cWHERE a.id = b.stu_idAND b.c_name = '计算机'AND a.id = c.stu_idAND c.c_name = '英语';-- 将计算机考试成绩按从高到低进行排序 SELECT s.name,e.*FROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.idWHERE c_name = '计算机'ORDER BY grade DESC;-- 从student表和score表中查询出学生的学号，然后合并查询结果 SELECT s.id FROM t_student AS sUNION SELECT e.stu_id FROM t_score AS e;-- 查询姓张或者姓王的同学的姓名、院系和考试科目及成绩 SELECT s.name,s.department,e.c_name,e.gradeFROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.idWHERE s.name LIKE '王%' OR s.name LIKE '张%';-- 查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩SELECT s.name,(year(NOW()) - s.birth) AS age,s.department,e.c_name,e.gradeFROM t_score AS eLEFT JOIN t_student AS sON e.stu_id = s.idWHERE s.address LIKE '%湖南%';