2017-10-20課堂代碼

2017-10-20課堂代碼-多表數據操作

創建五張表

1. 學生表t_student

id	code	name	id_card_number	clazz_id
1	01	張三	123	1
2	02	李四	456	1
3	01	王五	236	2
4	03	趙六	249	null

-- 創建學生表
DROP TABLE IF EXISTS t_student;
CREATE TABLE t_student(
    id              INT PRIMARY KEY AUTO_INCREMENT,
    code            VARCHAR(255),
    name            VARCHAR(255),
    id_card_number  VARCHAR(255),
    clazz_id        INT,
    CONSTRAINT fk_student_clazz FOREIGN KEY (clazz_id) REFERENCES t_clazz(id)
);

2.班級表t_clazz

id	name
1	Java96班
2	Java93班

-- 創建班級表
DROP TABLE IF EXISTS t_clazz;
CREATE TABLE t_clazz(
    id      INT PRIMARY KEY AUTO_INCREMENT,
    name    VARCHAR(255)
);

3.課程表t_course

id	name
1	HTML
2	CSS
3	JavaScript

DROP TABLE IF EXISTS t_course;
CREATE TABLE t_course(
    id      INT PRIMARY KEY AUTO_INCREMENT,
    name    VARCHAR(255)
);

4.賬號表t_account

id	student_id	userName	password
1	1	zhangsan	123456
2	2	lisi	123456
3	3	wangwu	123456

-- 創建學生賬號表
DROP TABLE IF EXISTS t_account;
CREATE TABLE t_account(
    id              INT PRIMARY KEY AUTO_INCREMENT,
    student_id      INT UNIQUE,
    userName        VARCHAR(255),
    password        VARCHAR(255),
    CONSTRAINT fk_account_student FOREIGN KEY (student_id) REFERENCES t_student(id)
);

5.學生課程表t_student_course

id	student_id	course_id
1	1	1
2	1	2
3	1	3
4	2	1
5	2	2

-- 創建學員課程中間表
DROP TABLE IF EXISTS t_student_course;
CREATE TABLE t_student_course(
    id              INT PRIMARY KEY AUTO_INCREMENT,
    student_id      INT,
    course_id       INT,
    CONSTRAINT fk_middle_student FOREIGN KEY (student_id) REFERENCES t_student(id),
    CONSTRAINT fk_middle_course FOREIGN KEY (course_id) REFERENCES t_course(id)
);

查詢語句

1.自然連接查詢，查詢學員學號，姓名，所在班級名稱

-- 自然連接查詢,查詢學員學號，姓名，所在班級名稱
SELECT s.clazz_id,s.code,s.name,c.id,c.name
FROM t_student AS s,t_clazz AS c
WHERE s.clazz_id = c.id;

2.內連接查詢

-- 內連接查詢
SELECT s.code AS '學號',s.name AS '姓名',c.name AS '班級名稱' FROM t_student AS s
INNER JOIN t_clazz AS c ON s.clazz_id = c.id;

3.左連接查詢

-- 左外連接，符合條件的被顯示，沒有的顯示null
SELECT s.code AS '學號',s.name AS '姓名',c.name AS '班級名稱' FROM t_student AS s
LEFT JOIN t_clazz AS c ON s.clazz_id = c.id;

4.綜合查詢

-- 綜合查詢，查詢學生班級，學號，姓名，賬號，賬號密碼，課程名稱
SELECT cl.name AS '班級名稱',s.code AS '學號',s.name AS '姓名',
a.userName AS '賬號名稱',a.password AS '密碼',c.name AS '課程名稱'
FROM t_student_course AS sc
LEFT JOIN t_student AS s ON sc.student_id = s.id
LEFT JOIN t_course AS c ON sc.course_id = c.id
LEFT JOIN t_clazz AS cl ON s.clazz_id = cl.id
LEFT JOIN t_account AS a ON a.student_id = s.id;