MySql学习笔记05——DML

DML

插入数据insert

insert into 表名(字段名1,字段名2,字段名3...)values(1,值2,值3)

字段名和值要一一对应(顺序对应,数据类型对应)

insert into t_student(no,name,sex,age,email) values(1,'Jack','b',12,'[email protected]');
+------+------+------+------+----------------+
| no   | name | sex  | age  | email          |
+------+------+------+------+----------------+
|    1 | Jack | b    |   12 | 123456@123.com |
+------+------+------+------+----------------+
insert into t_student(email,name,sex,age,no) values('[email protected]','lisi','f',20,2);
+------+------+------+------+----------------+
| no   | name | sex  | age  | email          |
+------+------+------+------+----------------+
|    1 | Jack | b    |   12 | 123456@123.com |
|    2 | lisi | f    |   20 | lisi@123.com   |
+------+------+------+------+----------------+
insert into t_student(no) values(3);
+------+------+------+------+----------------+
| no   | name | sex  | age  | email          |
+------+------+------+------+----------------+
|    1 | Jack | b    |   12 | 123456@123.com |
|    2 | lisi | f    |   20 | lisi@123.com   |
|    3 | NULL | NULL | NULL | NULL           |
+------+------+------+------+----------------+

insert语句只负责插入数据,不负责修改数据。

没有给其它字段指定值的话,默认值是NULL。

通过关键字default可以设置字段的默认值,例如:

sex char(1) default 'm',

insert语句中的字段名可以省略,但是values中的值就必须全部写上,并且一一对应。

insert插入时间

create table t_user(
    id int(11),
    name varchar(32),
    birth date
);
 insert into t_user values(123,'Jack',str_to_date('01-10-1990','%d-%m-%Y'));

使用str_to_date函数将字符串类型转换成data类型。

str_to_date('字符串日期','日期格式')

MySQL日期格式:

%Y    年// 注意这里Y大写
%m  月
%d  日
%h    时
%i    分
%s    秒

通常使用在插入insert方面,因为插入的时候需要一个日期类型的数据,需要通过该函数将字符串转换成date

如果你提供的日期字符串是%Y-%m-%d这个格式,str_to_date函数就不需要了!!!

查询的时候可以使用date-format函数将日期类型转化成特定格式的字符串。

date_format('日期类型数据', '日期格式')
mysql> select * from t_user;
+------+------+------------+
| id   | name | birth      |
+------+------+------------+
|  123 | Jack | 1990-10-01 |
|  124 | Lili | 1991-06-21 |
+------+------+------------+

默认的日期显示格式是%Y-%m-%d

自定义显示格式:

mysql> select id,name,date_format(birth,'%Y/%m/%d') as birth from t_user;
+------+------+------------+
| id   | name | birth      |
+------+------+------------+
|  123 | Jack | 1990/10/01 |
|  124 | Lili | 1991/06/21 |
+------+------+------------+

date和datetime之间的区别

date是短日期,只包括年月日

datetime是长日期,包括年月日,时分秒

mysql短日期默认格式:%Y-%m-%d
mysql长日期默认格式:%Y-%m-%d %h:%i:%s

create table t_user(
    id int,
    name varchar(32),
    birth date,
    create_time datetime
);

insert into t_user(id,name,birth,create_time) values(123,'Tim','1990-10-01','2021-06-21 12:12:52');
mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 1990-10-01 | 2021-06-21 12:12:52 |
+------+------+------------+---------------------+

now()函数可以获取系统的时间,并且是datetime类型的。

insert into t_user (id,name,birth,create_time) values(122,'Jan','2012-12-23',now());
mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 1990-10-01 | 2021-06-21 12:12:52 |
|  122 | Jan  | 2012-12-23 | 2022-07-17 12:28:10 |
|  111 | Nik  | 2011-06-23 | 2022-07-17 12:28:34 |
+------+------+------------+---------------------+

当然了,datetime也是支持函数date_format进行格式化显示的

mysql> select id,name,birth,date_format(create_time,'%h/%i/%s %Y-%m-%d')as create_time from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 1990-10-01 | 12/12/52 2021-06-21 |
|  122 | Jan  | 2012-12-23 | 12/28/10 2022-07-17 |
|  111 | Nik  | 2011-06-23 | 12/28/34 2022-07-17 |
+------+------+------------+---------------------+

修改表中数据update

update 表名 set 字段名1=新值1,字段名2=新值2,字段名3=新值3...where 条件

这里的where条件是用来判断修改哪一行的数据。

mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 1990-10-01 | 2021-06-21 12:12:52 |
|  122 | Jan  | 2012-12-23 | 2022-07-17 12:28:10 |
|  111 | Nik  | 2011-06-23 | 2022-07-17 12:28:34 |
+------+------+------------+---------------------+
update t_user set birth='2013-12-01',create_time=now() where id=123;
mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 2013-12-01 | 2022-07-17 12:58:55 |
|  122 | Jan  | 2012-12-23 | 2022-07-17 12:28:10 |
|  111 | Nik  | 2011-06-23 | 2022-07-17 12:28:34 |
+------+------+------------+---------------------+

如果没有了where条件,就是更新了所有。

 update t_user set create_time=now();
 mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 2013-12-01 | 2022-07-17 13:00:18 |
|  122 | Jan  | 2012-12-23 | 2022-07-17 13:00:18 |
|  111 | Nik  | 2011-06-23 | 2022-07-17 13:00:18 |
+------+------+------------+---------------------+

删除表中数据delete

delete from 表名 where 条件;

如果没有条件,整个表都会被删除!!

delete from t_user where id=111;
mysql> select * from t_user;
+------+------+------------+---------------------+
| id   | name | birth      | create_time         |
+------+------+------------+---------------------+
|  123 | Tim  | 2013-12-01 | 2022-07-17 13:00:18 |
|  122 | Jan  | 2012-12-23 | 2022-07-17 13:00:18 |
+------+------+------------+---------------------+

insert插入多条数据

insert into t_user (id,name,birth,create_time) values
(1,'zs','1980-10-11',now()), 
(2,'lisi','1981-10-11',now()),
(3,'wangwu','1982-10-11',now());
mysql> select * from t_user;
+------+--------+------------+---------------------+
| id   | name   | birth      | create_time         |
+------+--------+------------+---------------------+
|    1 | zs     | 1980-10-11 | 2022-07-17 13:41:43 |
|    2 | lisi   | 1981-10-11 | 2022-07-17 13:41:43 |
|    3 | wangwu | 1982-10-11 | 2022-07-17 13:41:43 |
+------+--------+------------+---------------------+

语法:

insert into t_user(字段名1,字段名2...) values
(),
(),
(),
();

快速创建表(复制表)

create table emp2 as select * from emp;
mysql> show tables;
+------------------------+
| Tables_in_bjpowernnode |
+------------------------+
| dept                   |
| emp                    |
| emp2                   |
| salgrade               |
| t_student              |
| t_user                 |
+------------------------+
mysql> select * from emp2;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME  | JOB       | MGR  | HIREDATE   | SAL     | COMM    | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
|  7369 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |    NULL |     20 |
|  7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     30 |
|  7521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     30 |
|  7566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |    NULL |     20 |
|  7654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     30 |
|  7698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |    NULL |     30 |
|  7782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |    NULL |     10 |
|  7788 | SCOTT  | ANALYST   | 7566 | 1987-04-19 | 3000.00 |    NULL |     20 |
|  7839 | KING   | PRESIDENT | NULL | 1981-11-17 | 5000.00 |    NULL |     10 |
|  7844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     30 |
|  7876 | ADAMS  | CLERK     | 7788 | 1987-05-23 | 1100.00 |    NULL |     20 |
|  7900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |    NULL |     30 |
|  7902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |    NULL |     20 |
|  7934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |    NULL |     10 |
+-------+--------+-----------+------+------------+---------+---------+--------+

原理是将一个查询结果当作一张新表,实现快速表的复制

create table mytable as select empno,ename from emp where job = 'MANAGER';
mysql> select * from mytable;
+-------+-------+
| empno | ename |
+-------+-------+
|  7566 | JONES |
|  7698 | BLAKE |
|  7782 | CLARK |
+-------+-------+

将查询结果插入到表中

用的不多,了解就行了。

create table dept_bak as select * from dept;
mysql> select * from dept_bak;
+--------+------------+----------+
| DEPTNO | DNAME      | LOC      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
insert into dept_bak select * from dept;
mysql> select * from dept_bak;
+--------+------------+----------+
| DEPTNO | DNAME      | LOC      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+

快速删除表中所有数据

使用delete不增加where条件也能删除表中所有数据

delete from dept_bak;
mysql> select * from dept_bak;
Empty set (0.00 sec)

但是它可以回滚数据:

mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from dept_bak;
+--------+------------+----------+
| DEPTNO | DNAME      | LOC      |
+--------+------------+----------+
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
|     10 | ACCOUNTING | NEW YORK |
|     20 | RESEARCH   | DALLAS   |
|     30 | SALES      | CHICAGO  |
|     40 | OPERATIONS | BOSTON   |
+--------+------------+----------+
8 rows in set (0.00 sec)

但是从底层逻辑上来说,delete是一个个来删除表中的数据,效率比较低。

另外一个快速删除表中所有数据的方法是truncate

truncate table 表名;

这个操作属于DDL中的操作。

使用truncate可以快速删除表中的所有数据,但是不支持数据回滚,因此要考虑再三再去使用它。

delete语句删除数据的原理?(delete属于DML语句!!!)
表中的数据被删除了,但是这个数据在硬盘上的真实存储空间不会被释放!!!
这种删除缺点是:删除效率比较低。
这种删除优点是:支持回滚,后悔了可以再恢复数据!!!
truncate语句删除数据的原理?
这种删除效率比较高,表被一次截断,物理删除。
这种删除缺点:不支持回滚。
这种删除优点:快速。

DDL中也有删除表的操作drop,但是drop是删除整个表,表和表的数据全部删除,truncate删除的仅仅只是表中的所有数据,表的结构还在。

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