SQL实战案例-优快云博客

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-- 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_student
GROUP 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 s
WHERE s.c_name IS NOT NULL
GROUP 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.grade
FROM t_score AS e
LEFT JOIN t_student AS s
ON e.stu_id = s.id
WHERE 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 e
LEFT JOIN t_student AS s
ON e.stu_id = s.id;
-- 计算每个学生的总成绩 
SELECT stu_id,SUM(grade)
FROM t_score
GROUP BY stu_id;
-- 计算每个考试科目的平均成绩 
SELECT c_name,AVG(grade)
FROM t_score
WHERE c_name IS NOT NULL
GROUP BY c_name;
-- 查询计算机成绩低于95的学生信息 
SELECT*
FROM t_score AS e
LEFT JOIN t_student AS s
ON e.stu_id = s.id
WHERE e.c_name = '计算机'
AND e.grade < 95;
-- 查询同时参加计算机和英语考试的学生的信息 
SELECT a.*
FROM t_student a,t_score b, t_score c
WHERE a.id = b.stu_id
AND b.c_name = '计算机'
AND a.id = c.stu_id
AND 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 e
LEFT JOIN t_student AS s
ON e.stu_id = s.id
WHERE 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 s
UNION 
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.grade
FROM t_score AS e
LEFT JOIN t_student AS s
ON e.stu_id = s.id
WHERE 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.grade
FROM t_score AS e
LEFT JOIN t_student AS s
ON e.stu_id = s.id
WHERE s.address LIKE '%湖南%';

-- 2.查询t_student表的所有记录
SELECT * FROM t_student;


-- 3.查询t_student表的第2条到4条记录
SELECT * FROM t_student LIMIT 1,3;


-- 4.从t_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;


-- 5.从t_student表中查询计算机系和英语系的学生的信息
SELECT * FROM t_student WHERE department IN ('计算机系','英语系');


-- 6.从t_student表中查询年龄18~22岁的学生信息
SELECT id,name,sex,2017-birth AS age,department,address
 FROM t_student
 WHERE 2017-birth BETWEEN  18 AND 22;


--  7.t_student表中查询每个院系有多少人 
SELECT department, COUNT(id) FROM t_student GROUP BY department;


-- 8. t_score表中查询每个科目的最高分
SELECT c_name,MAX(grade) FROM t_score GROUP BY c_name;


--  9.查询李四的考试科目（c_name）和考试成绩（grade）
 SELECT c_name, grade
  FROM t_score WHERE stu_id=
  (SELECT id FROM t_student
   WHERE name= '李四' );


--  10.用连接的方式查询所有学生的的信息和考试信息
SELECT t_student.id,name,sex,birth,department,address,c_name,grade
  FROM t_student,t_score
  WHERE t_student.id=t_score.stu_id;


--  11.计算每个学生的总成绩
SELECT  t_student.id,name,SUM(grade) FROM t_student,t_score
WHERE t_student.id=t_score.stu_id
GROUP BY id;


--  12.计算每个考试科目的平均成绩
SELECT c_name,AVG(grade) FROM t_score GROUP BY c_name;


--  13.查询计算机成绩低于95的学生信息
SELECT * FROM t_student
 WHERE id IN
 (SELECT stu_id FROM t_score
  WHERE c_name="计算机" and grade<95);

--  14.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' );


--  15.将计算机考试成绩按从高到低进行排序
SELECT stu_id, grade
  FROM t_score WHERE c_name= '计算机'
  ORDER BY grade DESC;


--  16.从t_student表和t_score表中查询出学生的学号，然后合并查询结果
SELECT id  FROM t_student
UNION
SELECT stu_id  FROM t_score;


--  17.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 t_student.id, name,sex,birth,department, address, c_name,grade
  FROM t_student, t_score
  WHERE
  (name LIKE  '张%'  OR name LIKE  '王%')
  AND
  t_student.id=t_score.stu_id ;


--  18.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 t_student.id, name,sex,birth,department, address, c_name,grade
   FROM t_student, t_score
   WHERE address LIKE '湖南%'   AND
    t_student.id=t_score.stu_id;