1. 数据操作增、删、改
2. 外键约束要求
3. 一对多表关系
4. 一对一表关系
5. 多对多表关系
6. 外键约束的参照操作
数据操作->插入数据
方法一:
INSERT [INTO] table_name [(column_name,...)]
{VALUES|VALUE} ({expr|DEFAULT},...),(...),...;
方法二:
INSERT [INTO] tbl_name SET col_name={expr|DEFAULT},...;
例如:
mysql> CREATE TABLE `tb1`(
-> `id` INT PRIMARY KEY AUTO_INCREMENT,
-> `name` VARCHAR(20) NOT NULL,
-> `age` INT DEFAULT 18
-> );
Query OK, 0 rows affected (0.54 sec)
mysql> INSERT INTO `tb1`(`name`)
-> VALUES('bank'),
-> ('tom')
-> ;
Query OK, 2 rows affected (0.08 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM `tb1`;
+----+-------+------+
| id | name | age |
+----+-------+------+
| 1 | bank | 18 |
| 2 | tom | 18 |
+----+-------+------+
2 rows in set (0.00 sec)
mysql> INSERT INTO `tb1` SET `name`='li';
Query OK, 1 row affected (0.07 sec)
mysql> INSERT INTO `tb1` SET `name`='lk',`age`=24;
Query OK, 1 row affected (0.07 sec)
数据操作->更新数据
UPDATE tb_name
SET col_name1={expr1|DEFAULT}[,col_name2={expr2|DEFAULT}]...
[WHERE where_condition];
例如:
mysql> SELECT * FROM `tb1`;
+----+--------+------+
| id | name | age |
+----+--------+------+
| 1 | bank | 18 |
| 2 | tom | 18 |
| 3 | li | 18 |
| 4 | lk | 24 |
+----+--------+------+
4 rows in set (0.00 sec)
mysql> UPDATE `tb1` SET `age`=`age`+1;
Query OK, 4 rows affected (0.06 sec)
Rows matched: 4 Changed: 4 Warnings: 0
mysql> UPDATE `tb1` SET `age`=20 WHERE `name`='lk';
Query OK, 1 row affected (0.10 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> UPDATE `tb1` SET `age`=21 WHERE `id`<3;
Query OK, 2 rows affected (0.10 sec)
Rows matched: 2 Changed: 2 Warnings: 0
mysql>
数据操作->删除数据
DELETE FROM tbl_name [WHERE where_conditon];
tip:不添加WHERE则会删除全部记录
例如:
mysql> SELECT * FROM `tb1`;
+----+--------+------+
| id | name | age |
+----+--------+------+
| 1 | bank | 21 |
| 2 | tom | 21 |
| 3 | lk | 21 |
| 4 | li | 26 |
+----+--------+------+
4 rows in set (0.00 sec)
mysql> DELETE FROM `tb1` WHERE `id`=4;
Query OK, 1 row affected (0.06 sec)
mysql> DELETE FROM `tb1`;
Query OK, 3 rows affected (0.13 sec)
mysql> SELECT * FROM `tb1`;
Empty set (0.00 sec)
mysql>
修改表中的列名
mysql> DESC tb1;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(20) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> ALTER TABLE `tb1`
-> CHANGE `name` `mingzi` VARCHAR(10) NOT NULL;
Query OK, 2 rows affected (0.04 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> DESC tb1;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
|mingzi | varchar(10) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql>
外键约束FOREIGN KEY
外键约束FOREIGN KEY，保持数据一致性，完整性实现一对一或一对多关系。
外键约束的要求:
数据表的存储引擎只能为InnoDB
外键列和参照数据类型一致
外键必须关联到键上面去
ALTER TABLE yourtablename
ADD [CONSTRAINT 外键名] FOREIGN KEY [id] (index_col_name, ...)
REFERENCES tbl_name (index_col_name, ...)
[ON DELETE {CASCADE | SET NULL | NO ACTION | RESTRICT}]
[ON UPDATE {CASCADE | SET NULL | NO ACTION | RESTRICT}]
一对多关系
例如，学校中一个学院可以有很多的学生，而一个学生只属于某一个学院（通常情况下），学院与学生之间的关系就是一对多的关系，通过外键关联来实现这种关系。
例如:
创建学院表：
mysql> CREATE TABLE `department`(
-> `id` INT PRIMARY KEY AUTO_INCREMENT,
-> `name` VARCHAR(15) NOT NULL
-> );
Query OK, 0 rows affected (0.61 sec)
创建学生表：
mysql> CREATE TABLE `student`(
-> `id` INT PRIMARY KEY AUTO_INCREMENT,
-> `name` VARCHAR(20) NOT NULL,
-> `dept_id` INT,
-> FOREIGN KEY (`dept_id`) REFERENCES `department`(`id`)
-> );
Query OK, 0 rows affected (0.51 sec)
插入数据
mysql> INSERT INTO `department`(`name`)
-> VALUES('A'),
-> ('B')
-> ;
Query OK, 2 rows affected (0.10 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> INSERT INTO `student`(`name`,`dept_id`)
-> VALUES('a1',1),
-> ('a2',2),
-> ('a3',2)
-> ;
Query OK, 3 rows affected (0.08 sec)
Records: 3 Duplicates: 0 Warnings: 0
一对一关系
例如:学生表中有学号、姓名、学院，但学生还有些比如电话，家庭住址等比较私密的信息，这些信息不会放在学生表当中，会新建一个学生的详细信息表来存放。这时的学生表和学生的详细信息表两者的关系就是一对一的关系，因为一个学生只有一条详细信息。用外键加主键的方式来实现这种关系。
例：
学生表：
mysql> DESC `student`;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| dept_id | int(11) | YES | MUL | NULL | |
+---------+-------------+------+-----+---------+----------------+
3 rows in set (0.06 sec)
建立详细学生表：
mysql> CREATE TABLE `student_details`(
-> `id` INT PRIMARY KEY,
-> `age` INT,
-> `gender` CHAR(1),
-> FOREIGN KEY (`id`) REFERENCES `student`(`id`)
-> );
Query OK, 0 rows affected (0.67 sec)
mysql>
多对多关系
例如:学生要报名选修课，一个学生可以报名多门课程，一个课程有很多的学生报名，那么学生表和课程表两者就形成了多对多关系。对于多对多关系，需要创建第三张关系表，关系表中通过外键加主键的形式实现这种关系。
例如:
建立课程表：
mysql> CREATE TABLE `course`(
-> `id` INT PRIMARY KEY AUTO_INCREMENT,
-> `name` VARCHAR(20) NOT NULL,
-> );
Query OK, 0 rows affected (1.18 sec)
学生与课程多对多关系表
mysql> CREATE TABLE `select`(
-> `s_id` INT,
-> `crs_id` INT,
-> PRIMARY KEY (`s_id`,`crs_id`),
-> FOREIGN KEY (`s_id`) REFERENCES `student` (`id`),
-> FOREIGN KEY (`crs_id`) REFERENCES `course` (`id`)
-> );
Query OK, 0 rows affected (0.50 sec)
外键约束的参照操作
1.CASCADE从父表删除或更新时自动删除或更新子表中的匹配行
2.SET NULL从父表删除或更新行时，设置子表中的外键列为NULL。
如果使用该选项，必须保证子表列没有指定NOT NULL
3.RESTRICT拒绝对父表的删除或更新操作
4.NO ACTION标准的SQL关键字，在mysql中与RESTRICT作用相同
on delete RESTRICT | on update CASCADE
例如:
mysql> ALTER TABLE `students`
-> DROP FOREIGN KEY `students_ibfk_1`
-> ;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE `students`
-> ADD CONSTRAINT `stu_ibfk_1` FOREIGN KEY(`dept_id`) REFERENCES `department`(`d_id`) ON UPDATE CASCADE;
Query OK, 3 rows affected (0.04 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> UPDATE `department` SET `d_id`=4 WHERE `name`='A';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> SELECT * FROM `students`;
+------+------+---------+
| s_id | name | dept_id |
+------+------+---------+
| 1 | a1 | 4 |
| 2 | a2 | 2 |
| 3 | a3 | 2 |
+------+------+---------+
3 rows in set (0.00 sec)
mysql>