sql之DML数据操作语言
目录
DML数据操作语言（insert、delete、update）
1.insert 命令
1）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)
2）插入数据（不规范写法）
mysql> insert into student values(1,'邱导',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 | 邱导 | 78 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
1 row in set (0.00 sec)
3）插入数据（规范写法）
#1.插入指定列数据
mysql> insert into student(name,age) values('曾导','84');
Query OK, 1 row affected (0.00 sec)
mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name | age | gender | cometime | birthday |
+----+--------+-----+--------+---------------------+---------------------+
| 1 | 邱导 | 78 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 78 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 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('曾导','84','1936-02-20');
Query OK, 1 row affected (0.00 sec)
mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name | age | gender | cometime | birthday |
+----+--------+-----+--------+---------------------+---------------------+
| 1 | 邱导 | 78 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 78 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
4 rows in set (0.00 sec)
4）插入多条数据
mysql> insert into student(name,age,birthday) values('好大','18',1936-02-21),('好小','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 | 邱导 | 78 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 78 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
| 8 | 好小 | 28 | f | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)
2.update命令
1）查看数据
mysql> select * from student;
+----+--------+-----+--------+---------------------+---------------------+
| id | name | age | gender | cometime | birthday |
+----+--------+-----+--------+---------------------+---------------------+
| 1 | 邱导 | 78 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 78 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
| 8 | 好小 | 28 | f | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)
2）修改数据
#使用update语句必须要加where条件
mysql> update student set age=18 where name='邱导';
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 | 邱导 | 18 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 18 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
| 8 | 好小 | 28 | f | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)
3）指定修改一条数据
#如果数据库有主键，一定使用主键来作为where判断
mysql> update student set age=88 where name='邱导' 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 | 邱导 | 88 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 88 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 |
| 8 | 好小 | 28 | f | 2020-07-15 09:31:07 | 1992-01-01 00:00:00 |
+----+--------+-----+--------+---------------------+---------------------+
8 rows in set (0.00 sec)
3.delete语句
1）删除数据
#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 | 邱导 | 88 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 |
| 2 | 邱导 | 88 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 |
| 7 | 好大 | 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
4.使用update代替delete
1）添加状态字段
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 | 邱导 | 88 | f | 2020-07-15 09:21:12 | 1942-07-14 00:00:00 | 1 |
| 2 | 邱导 | 88 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 1 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL | 1 |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1 |
+----+--------+-----+--------+---------------------+---------------------+--------+
7 rows in set (0.00 sec)
2）使用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 | 邱导 | 88 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 0 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL | 1 |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1 |
+----+--------+-----+--------+---------------------+---------------------+--------+
6 rows in set (0.00 sec)
#相当于学生回来
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 | 邱导 | 88 | f | 2020-07-15 09:22:27 | 1942-07-14 00:00:00 | 1 |
| 3 | 曾导 | 84 | f | 2020-07-15 09:24:17 | NULL | 1 |
| 4 | 曾导 | 84 | f | 2020-07-15 09:25:22 | 1936-02-20 00:00:00 | 1 |
| 5 | 曾导 | 84 | f | 2020-07-15 09:28:11 | 1936-02-21 00:00:00 | 1 |
| 6 | 好大 | 18 | f | 2020-07-15 09:29:18 | 0000-00-00 00:00:00 | 1 |
| 7 | 好大 | 18 | f | 2020-07-15 09:31:07 | 0000-00-00 00:00:00 | 1 |
+----+--------+-----+--------+---------------------+---------------------+--------+
6 rows in set (0.00 sec)
5. drop，truncate，delete区别
1、drop (删除表)：删除内容和定义，释放空间。简单来说就是把整个表去掉.以后要新增数据是不可能的,除非新增一个表。
drop语句将删除表的结构被依赖的约束（constrain),触发器（trigger)索引（index);依赖于该表的存储过程/函数将被保留，但其状态会变为：invalid。
2、truncate (清空表中的数据)：删除内容、释放空间但不删除定义(保留表的数据结构)。与drop不同的是,只是清空表数据而已。
truncate 不能删除行数据,要删就要把表清空。
3、delete (删除表中的数据)：delete 语句用于删除表中的行。delete语句执行删除的过程是每次从表中删除一行，并且同时将该行的删除操作作为事务记录在日志中保存以便进行进行回滚操作。
truncate与不带where的delete ：只删除数据，而不删除表的结构（定义）
4、truncate table 删除表中的所有行，但表结构及其列、约束、索引等保持不变。新行标识所用的计数值重置为该列的种子。如果想保留标识计数值，请改用delete。
如果要删除表定义及其数据，请使用 drop table 语句。
5、对于由foreign key约束引用的表，不能使用truncate table ，而应使用不带where子句的delete语句。由于truncate table 记录在日志中，所以它不能激活触发器。
6、执行速度，一般来说: drop> truncate > delete。
7、delete语句是数据库操作语言(dml)，这个操作会放到 rollback segement 中，事务提交之后才生效；如果有相应的 trigger，执行的时候将被触发。
truncate、drop 是数据库定义语言(ddl)，操作立即生效，原数据不放到 rollback segment 中，不能回滚，操作不触发 trigger。
