MySQL数据库应用与管理

1. 子查询的返回值为单列单值
例1：查询与学号（sNo）为“1308013101”的同学在同一个班级的学生名单。
代码展示

SELECT *
FROM student
WHERE deptName = (
SELECT deptName
FROM student
WHERE sNo = "1308013101");```

例2：查询选修课程编号（cNo）为“01001”的课程且成绩超过该课程平均分的学生的学号、姓名、班级、课程名称和成绩。

SELECT sNo,sName,deptName,cName,grade
FROM course JOIN score ON course.id = score.cId
JOIN student ON student.id = score.sId
WHERE cNo ="01001" AND grade > (
SELECT AVG(grade)
FROM course JOIN score ON course.id = score.cId
WHERE cNo ="01001"
)

这道题代码不是很难，比较困难的是分析题目，和条件比对。

2. 子查询的返回值为单列多值
例1：查询选修课程编号（cNo）为“01001”的课程的学生名单。

SELECT *
FROM student
WHERE id IN
(SELECT sId
FROM score JOIN course ON score.cId = course.id
WHERE cNo="01001");

例2：查询学号为“1308013101”的学生选修的课程信息。

SELECT*FROM course
WHERE id IN(SELECT cId FROM score
JOIN student ON student.id=score.sId AND sNo='1308013101');

例3：查询没有选修课程的女生名单。

SELECT*FROM student
WHERE sex='女'
AND id NOT IN(SELECT sId FROM score);

例4：查询“软件131“班中比”网络131”班中所有学生年龄都要大的学生信息。

SELECT*
FROM student
WHERE deptName = "软件131" AND birthday <(
SELECT MIN(birthday)
FROM student
WHERE deptName = "网络131"
);

SELECT*
FROM student
WHERE deptName = "软件131" AND birthday < ALL(
SELECT birthday
FROM student
WHERE deptName = "网络131"
);

例5：查询非“网络131“班中比”网络131”班中任意一个学生年龄大的学生信息。

SELECT*
FROM student
WHERE deptName != "网络131" AND birthday < (
SELECT MAX(birthday)
FROM student
WHERE deptName = "网络131"
);

. 子查询的返回值为多列数据
例1：查询选修课程的女生名单，使用关键字EXISTS。

SELECT *
FROM student
WHERE sex = "女" AND EXISTS(
SELECT *
FROM score
WHERE student.id =score.sId);

五、带子查询的数据更新

例1：创建数据表tempStudent，包含5个字段：学生ID（id）、学号（stuNo）、姓名（stuName）性别（sex）和班级名称（deptName）；查询“网络131”班的学生记录，将查询结果插入到tempStudent表中。

CREATE TABLE tempStudent(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
stuNo CHAR(10) NOT NULL,
stuName VARCHAR(20) NOT NULL,
sex CHAR(2) NOT NULL,
deptName VARCHAR(30) NOT NULL,
PRIMARY KEY(id)
);

INSERT INTO tempStudent
SELECT id,sNo,sName,sex,deptName
FROM student
WHERE deptName ="网络131";

例2：将“数据结构”课程的成绩统一减去5分。

UPDATE score
SET grade = grade - 5
WHERE cId =(
SELECT id
FROM course
WHERE cName ="数据结构"
);

例3：将“机电131”班的学生成绩记录全部删除。

DELETE FROM score
WHERE   sId IN
(SELECT id
FROM student
WHERE deptName = "机电131")