MySQL学习日志十，子查询和嵌套查询

Posted 2023-05-14 yzx-sir

子查询

where(这个值是计算出来的)
先执行where里面的语句，之后执行外面的语句

本质：where里面嵌套一个子查询语句

查询参加高等数学考试的学生（学号，姓名。科目编号，成绩）,降序排列

-- 方式一：连接查询

SELECT s.studentno,studentname,r.subjectno,studentresult
FROM student s
INNER JOIN result r
on s.studentno=r.studentno
INNER JOIN `subject`sub
on sub.subjectno=r.subjectno
WHERE subjectname=\'高等数学-1\'
order by studentresult DESC

-- 方式二：子查询

SELECT s.studentno,studentname,r.subjectno,studentresult
FROM student s
INNER JOIN result r
on s.studentno=r.studentno
WHERE subjectno=(
SELECT subjectno from `subject` WHERE subjectname=\'高等数学-1\'
)
order by studentresult DESC

-- 查询分数不小于80的学生的学号，姓名

SELECT s.studentno,studentname
from student s
INNER JOIN result r
on s.studentno=r.studentno
WHERE studentresult>=80

-- 查询参加高等数学-1分数不小于80的学生的学号，姓名

SELECT s.studentno,studentname
from student s
INNER JOIN result r
on s.studentno=r.studentno
WHERE studentresult>=80
 and 
subjectno=(
SELECT subjectno from `subject` WHERE subjectname=\'高等数学-1\'
)

-- 查询参加高等数学-1分数不小于80的学生的学号，姓名
-- 嵌套查询(由里及外)

SELECT studentno,studentname
from student
WHERE studentno in(
SELECT studentno FROM result WHERE studentresult>=80
 and 
subjectno=(
SELECT subjectno from `subject` WHERE subjectname=\'高等数学-1\'
))

-- 查询参加高等数学-1，前5名同学的信息（学号，姓名，成绩）
-- 联表查询

SELECT s.studentno,studentname,studentresult
from student s
INNER JOIN result r
on s.studentno=r.studentno
INNER JOIN `subject` sub
ON r.subjectno=sub.subjectno
WHERE subjectname=\'高等数学-1\'
ORDER BY studentresult DESC
LIMIT 0,5

-- 查询参加高等数学-1，前5名同学的信息（学号，姓名，成绩）
-- 子查询

SELECT s.studentno,studentname,studentresult
from student s
INNER JOIN result r
on s.studentno=r.studentno
WHERE subjectno= (
SELECT subjectno from `subject` WHERE subjectname=\'高等数学-1\'
)
ORDER BY studentresult DESC
LIMIT 0,5

MYSQL初级学习笔记六：子查询！（视频序号：初级_37-41)

知识点八：子查询(42)

什么是子查询：

　　子查询是将一个查询语句嵌套在另一个查询语句中。内层查询语句的查询结果，可以作为外层查询语句提供条件。

引发子查询的情况：

　　使用[NOT] IN 的子查询

 1 --删除原本的员工表和部门表，重新建
 2 DROP TABLE employee,department;
 3 
 4 CREATE TABLE IF NOT EXISTS department(
 5 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
 6 depName VARCHAR(20) NOT NULL UNIQUE
 7 )ENGINE=INNODB;
 8 
 9 INSERT department(depName) VALUES(‘教学部‘),
10 (‘市场部‘),
11 (‘运营部‘),
12 (‘督导部‘);
13 
14 -- 创建员工表employee(子表)
15 -- id ,username ,depId
16 CREATE TABLE IF NOT EXISTS employee(
17 id SMALLINT UNSIGNED AUTO_INCREMENT KEY,
18 username VARCHAR(20) NOT NULL UNIQUE,
19 depId TINYINT UNSIGNED
20 )ENGINE=INNODB;
21 
22 INSERT employee(username,depId) VALUES(‘king‘,1),
23 (‘queen‘,2),
24 (‘张三‘,3),
25 (‘李四‘,4),
26 (‘王五‘,1);
27 
28 -- 由[NOT] IN引发的子查询
29 SELECT id FROM department;
30 
31 SELECT id,username FROM employee WHERE depId IN(1,2,3,4);
32 
33 SELECT id,username FROM employee WHERE depId IN(SELECT id FROM department);
34 
35 SELECT id,username FROM employee WHERE depId NOT IN(SELECT id FROM department);
36 
37 INSERT employee(username,depId) VALUES(‘testtest‘,8);

测试[NOT IN]子查询

　　使用比较运算符的子查询：

　　　　=，>,<,>=,<=,<>,!=,ó

　　使用[NOT] EXISTS的子查询：

 1 --　创建学员表student
 2 -- id username score
 3 CREATE TABLE IF NOT EXISTS student(
 4 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
 5 username VARCHAR(20)  NOT NULL UNIQUE,
 6 score TINYINT UNSIGNED
 7 );
 8 INSERT student(username,score) VALUES(‘king‘,95),
 9 (‘king1‘,35),
10 (‘king2‘,45),
11 (‘king3‘,55),
12 (‘king4‘,65),
13 (‘king5‘,75),
14 (‘king6‘,80),
15 (‘king7‘,90),
16 (‘king8‘,25);
17 -- 创建奖学金scholarship
18 -- id ,level
19 
20 CREATE TABLE IF NOT EXISTS scholarship(
21 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
22 level TINYINT UNSIGNED
23 );
24 INSERT scholarship(level) VALUES(90),(80),(70);
25 
26 
27 -- 查询获得1等奖学金的学员有
28 
29 SELECT level FROM scholarship WHERE id=1;
30 
31 SELECT id,username FROM student WHERE score>=90;
32 
33 SELECT id,username FROM student WHERE score>=(SELECT level FROM scholarship WHERE id=1);
34 
35 -- 查询部门表中
36 
37 SELECT * FROM department WHERE id=5;
38 
39 SELECT id,username FROM employee WHERE EXISTS(SELECT * FROM department WHERE id=5);
40 
41 SELECT id,username FROM employee WHERE EXISTS(SELECT * FROM department WHERE id=4);
42 
43 SELECT id,username FROM employee WHERE NOT EXISTS(SELECT * FROM department WHERE id=41);

比较运算符与[NOT] EXISTS测试

　　使用ANY | SOME 或者ALL的子查询：

运算符                关键字	ANY	SOME	ALL
>，>=	最小值	最小值	最大值
<，<=	最大值	最大值	最小值
=	任意值	任意值
<>，!=			任意值

 1 -- 查询所有获得奖学金的学员
 2 
 3 SELECT id,username,score FROM student WHERE score>=ANY(SELECT level FROM scholarship);
 4 
 5 
 6 SELECT id,username,score FROM student WHERE score>=SOME(SELECT level FROM scholarship);
 7 
 8 -- 查询所有学员中获得一等奖学金的学员
 9 SELECT id,username,score FROM student WHERE score >=ALL(SELECT level FROM scholarship);
10 
11 -- 查询学员表中没有获得奖学金的学员
12 
13 SELECT id,username,score FROM student WHERE score<ALL(SELECT level FROM scholarship);
14 
15 
16 SELECT id,username,score FROM student WHERE score<ANY(SELECT level FROM scholarship);
17 
18 SELECT id,username,score FROM student WHERE score<=ANY(SELECT level FROM scholarship);
19 
20 -- 相当于IN
21 SELECT id,username,score FROM student WHERE score=ANY(SELECT level FROM scholarship);
22 
23 SELECT id,username,score FROM student WHERE score IN(SELECT level FROM scholarship);
24 
25 -- 相当于NOT IN
26 SELECT id,username,score FROM student WHERE score NOT IN(SELECT level FROM scholarship);
27 
28 SELECT id,username,score FROM student WHERE score <> ALL(SELECT level FROM scholarship);

ANY,SOME,ALL测试

 

将查询结果写入到数据表：

　　INSERT [INTO] tbl_name [(col_name,…)] SELECT …

建数据表同时将查询结果写入到数据表：

　　CREATE TABLE [IF NOT EXISTS] tbl_name

　　[(create_definition,…)]

　　select_statement

 1 --将查询结果写入到数据表
 2 CREATE TABLE test1 (
 3 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
 4 num TINYINT UNSIGNED
 5 );
 6 INSERT test1(id,num) 
 7 SELECT id,score FROM student;
 8 
 9 
10 CREATE TABLE test2 (
11 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
12 num TINYINT UNSIGNED
13 )SELECT id,score FROM student;
14 
15 CREATE TABLE test3 (
16 id TINYINT UNSIGNED AUTO_INCREMENT KEY,
17 score TINYINT UNSIGNED
18 )SELECT id,score FROM student;

将查询结果写入到数据表测试