MYSQL初级学习笔记六：子查询！（视频序号：初级_42 | 43)

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

--删除原本的员工表和部门表，重新建
DROP TABLE employee,department;

CREATE TABLE IF NOT EXISTS department(
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
depName VARCHAR(20) NOT NULL UNIQUE
)ENGINE=INNODB;

INSERT department(depName) VALUES('教学部'),
('市场部'),
('运营部'),
('督导部');

-- 创建员工表employee(子表)
-- id ,username ,depId
CREATE TABLE IF NOT EXISTS employee(
id SMALLINT UNSIGNED AUTO_INCREMENT KEY,
username VARCHAR(20) NOT NULL UNIQUE,
depId TINYINT UNSIGNED
)ENGINE=INNODB;

INSERT employee(username,depId) VALUES('king',1),
('queen',2),
('张三',3),
('李四',4),
('王五',1);

-- 由[NOT] IN引发的子查询
SELECT id FROM department;

SELECT id,username FROM employee WHERE depId IN(1,2,3,4);

SELECT id,username FROM employee WHERE depId IN(SELECT id FROM department);

SELECT id,username FROM employee WHERE depId NOT IN(SELECT id FROM department);

INSERT employee(username,depId) VALUES('testtest',8);

　　使用比较运算符的子查询：

　　　　=，>,<,>=,<=,<>,!=,ó

　　使用[NOT] EXISTS的子查询：

--　创建学员表student
-- id username score
CREATE TABLE IF NOT EXISTS student(
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
username VARCHAR(20)  NOT NULL UNIQUE,
score TINYINT UNSIGNED
);
INSERT student(username,score) VALUES('king',95),
('king1',35),
('king2',45),
('king3',55),
('king4',65),
('king5',75),
('king6',80),
('king7',90),
('king8',25);
-- 创建奖学金scholarship
-- id ,level

CREATE TABLE IF NOT EXISTS scholarship(
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
level TINYINT UNSIGNED
);
INSERT scholarship(level) VALUES(90),(80),(70);


-- 查询获得1等奖学金的学员有

SELECT level FROM scholarship WHERE id=1;

SELECT id,username FROM student WHERE score>=90;

SELECT id,username FROM student WHERE score>=(SELECT level FROM scholarship WHERE id=1);

-- 查询部门表中

SELECT * FROM department WHERE id=5;

SELECT id,username FROM employee WHERE EXISTS(SELECT * FROM department WHERE id=5);

SELECT id,username FROM employee WHERE EXISTS(SELECT * FROM department WHERE id=4);

SELECT id,username FROM employee WHERE NOT EXISTS(SELECT * FROM department WHERE id=41);

　　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

-- 查询所有获得奖学金的学员

SELECT id,username,score FROM student WHERE score>=ANY(SELECT level FROM scholarship);


SELECT id,username,score FROM student WHERE score>=SOME(SELECT level FROM scholarship);

-- 查询所有学员中获得一等奖学金的学员
SELECT id,username,score FROM student WHERE score >=ALL(SELECT level FROM scholarship);

-- 查询学员表中没有获得奖学金的学员

SELECT id,username,score FROM student WHERE score<ALL(SELECT level FROM scholarship);


SELECT id,username,score FROM student WHERE score<ANY(SELECT level FROM scholarship);

SELECT id,username,score FROM student WHERE score<=ANY(SELECT level FROM scholarship);

-- 相当于IN
SELECT id,username,score FROM student WHERE score=ANY(SELECT level FROM scholarship);

SELECT id,username,score FROM student WHERE score IN(SELECT level FROM scholarship);

-- 相当于NOT IN
SELECT id,username,score FROM student WHERE score NOT IN(SELECT level FROM scholarship);

SELECT id,username,score FROM student WHERE score <> ALL(SELECT level FROM scholarship);

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

--将查询结果写入到数据表
CREATE TABLE test1 (
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
num TINYINT UNSIGNED
);
INSERT test1(id,num) 
SELECT id,score FROM student;


CREATE TABLE test2 (
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
num TINYINT UNSIGNED
)SELECT id,score FROM student;

CREATE TABLE test3 (
id TINYINT UNSIGNED AUTO_INCREMENT KEY,
score TINYINT UNSIGNED
)SELECT id,score FROM student;