DML 数据操纵语言

目录

• 插入数据（INSERT）
  • 插入数据（不规范）
  • 插入数据（规范）
  • 插入多条数据（规范）
• 修改数据（UPDATE）
  • 修改数据
  • 指定修改数据
• 删除数据（DELETE）
• 案例：UPDATE 代替 DELETE
  • 添加状态字段 STATUS
  • UPDATE 代替 DELETE

插入数据（INSERT）

#  查看表结构
mysql> desc student;
+----------+---------------------+------+-----+-------------------+----------------+
| Field    | Type                | Null | Key | Default           | Extra          |
+----------+---------------------+------+-----+-------------------+----------------+
| id       | int(11)             | NO   | PRI | NULL              | auto_increment |
| name     | varchar(12)         | NO   |     | NULL              |                |
| age      | tinyint(3) unsigned | NO   |     | NULL              |                |
| gender   | enum('m','f')       | YES  |     | f                 |                |
| cometime | datetime            | YES  |     | CURRENT_TIMESTAMP |                |
| birthday | datetime            | YES  |     | NULL              |                |
+----------+---------------------+------+-----+-------------------+----------------+
6 rows in set (0.00 sec)

插入数据（不规范）

mysql> insert into student values(1,'小王',78,'f',now(),'1942-07-14');
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  78 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
1 row in set (0.00 sec)

插入数据（规范）

# 1.插入指定列数据
mysql> insert into student(name,age) values('小张','84');
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  78 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  78 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
+----+--------+-----+--------+---------------------+---------------------+
3 rows in set (0.00 sec)

# 2.插入指定列数据
mysql> insert into student(name,age,birthday) values('小张','84','1936-02-20');
Query OK, 1 row affected (0.00 sec)

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  78 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  78 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
4 rows in set (0.00 sec)

插入多条数据（规范）

mysql> insert into student(name,age,birthday) values('小李','18',1936-02-21),('小六','28','1992-01-01');
Query OK, 2 rows affected, 1 warning (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 1

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  78 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  78 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
|  8 | 小六   |  28 | f      | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)

修改数据（UPDATE）

#  查看表数据
mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  78 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  78 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
|  8 | 小六   |  28 | f      | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)

修改数据

# 使用update语句必须要加where条件
mysql> update student set age=18 where name='小王';
Query OK, 2 rows affected (0.01 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  18 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  18 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
|  8 | 小六   |  28 | f      | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)

指定修改数据

# 如果数据库有主键，一定使用主键
mysql> update student set age=88 where name='小王' and cometime='2020-07-15 09:21:12';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> update student set age=88 where id=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  88 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  88 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
|  8 | 小六   |  28 | f      | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)

删除数据（DELETE）

# 1.先查看数据，确认要删除的数据，怎么确定唯一

# 2.使用delete语句也一定要加where条件
mysql> delete from student where id=8;
Query OK, 1 row affected (0.01 sec)

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name   | age | gender | cometime            | birthday            |
+----+--------+-----+--------+---------------------+---------------------+
|  1 | 小王   |  88 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
|  2 | 小王   |  88 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
7 rows in set (0.00 sec)

# 3.如果就是要清空表
mysql> delete from student where 1=1;
Query OK, 1 row affected (0.01 sec)
# (危险)
truncate table student;
drop table student

案例：UPDATE 代替 DELETE

如果某个学生辍学，数据库中不会真正的删除这个学生的记录，一般通过一个字段判断某个学生是否退学，如下案例，通过 status 的值判断该学生是否在学校上课，如果是 1 则表示在读，是 0 则表示辍学，那么使用 UPDATE 即可实现 “删除” 此学生记录的功能 。

添加状态字段 STATUS

mysql> alter table student add status enum('1','0') default 1;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+--------+
| id | name   | age | gender | cometime            | birthday            | status |
+----+--------+-----+--------+---------------------+---------------------+--------+
|  1 | 小王   |  88 | f      | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 | 1      |
|  2 | 小王   |  88 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 1      |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                | 1      |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1      |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1      |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1      |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1      |
+----+--------+-----+--------+---------------------+---------------------+--------+
7 rows in set (0.00 sec)

UPDATE 代替 DELETE

# 相当于删除学生
mysql> update student set status='0' where id =2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+--------+
| id | name   | age | gender | cometime            | birthday            | status |
+----+--------+-----+--------+---------------------+---------------------+--------+
|  2 | 小王   |  88 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 0      |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                | 1      |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1      |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1      |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1      |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1      |
+----+--------+-----+--------+---------------------+---------------------+--------+
6 rows in set (0.00 sec)

# 相当于学生返校继续读书
mysql> update student set status='1' where id =2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+--------+
| id | name   | age | gender | cometime            | birthday            | status |
+----+--------+-----+--------+---------------------+---------------------+--------+
|  2 | 小王   |  88 | f      | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 1      |
|  3 | 小张   |  84 | f      | 2020-07-15 09:24:17 | NULL                | 1      |
|  4 | 小张   |  84 | f      | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1      |
|  5 | 小张   |  84 | f      | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1      |
|  6 | 小李   |  18 | f      | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1      |
|  7 | 小李   |  18 | f      | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1      |
+----+--------+-----+--------+---------------------+---------------------+--------+
6 rows in set (0.00 sec)