mysql语句-DML语句

DML语句

DML是指对数据库中表记录的操作，主要包括数据的增删改查以及更新，下面依次介绍

首先创建一张表:：
表名：emp
字段：ename varchar(20),hiredate date ,sal decimal(10,2), deptno int(3)

mysql> create table emp(
    -> ename varchar(20),
    -> hiredate date,
    -> sal decimal(10,2),
    -> deptno int(3));
Query OK, 0 rows affected (0.02 sec)

mysql> desc emp;
+----------+---------------+------+-----+---------+-------+
| Field    | Type          | Null | Key | Default | Extra |
+----------+---------------+------+-----+---------+-------+
| ename    | varchar(20)   | YES  |     | NULL    |       |
| hiredate | date          | YES  |     | NULL    |       |
| sal      | decimal(10,2) | YES  |     | NULL    |       |
| deptno   | int(3)        | YES  |     | NULL    |       |
+----------+---------------+------+-----+---------+-------+
4 rows in set (0.01 sec)

1、insert插入记录

语法：insert into 表名(可选字段传值) values(与前面字段对应填值)
不指定字段名时顺序一一对应全要传值。
列如：

insert into emp values('kingfan','2018-10-23','2000',1);

mysql> insert into emp values('kingfan','2018-10-23','2000',1);
Query OK, 1 row affected (0.01 sec)

#使用查询语句查看添加记录
mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| kingfan | 2018-10-23 | 2000.00 |      1 |
+---------+------------+---------+--------+
1 row in set (0.00 sec)

mysql还支持多条语句同时插入：

mysql> insert into emp values('rnf','2000-1-1','3000','2'),('edg','2000-1-1','4000',1);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| kingfan | 2018-10-23 | 2000.00 |      1 |
| rnf     | 2000-01-01 | 3000.00 |      2 |
| edg     | 2000-01-01 | 4000.00 |      1 |
+---------+------------+---------+--------+
3 rows in set (0.00 sec)

注意每条记录之间要逗号隔开

更新记录update

对于表中的记录的值可以通过update命令来修改
语法1: update 表名 set 字段名=修改值 where 字段名=值；where是筛选条根据条件把找到的记录然后将set后面的字段名设定成指定值。
语法2:update 表名 set 字段名=修改值 where 字段名 like 值；
语法1：将enmae=kingfan的记录的ename改成Kingfan

mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| kingfan | 2018-10-23 | 2000.00 |      1 |
| rnf     | 2000-01-01 | 3000.00 |      2 |
| edg     | 2000-01-01 | 4000.00 |      1 |
+---------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> update emp set ename='KingFan' where ename='kingfan';
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| KingFan | 2018-10-23 | 2000.00 |      1 |
| rnf     | 2000-01-01 | 3000.00 |      2 |
| edg     | 2000-01-01 | 4000.00 |      1 |
+---------+------------+---------+--------+
3 rows in set (0.00 sec)

语法2：

mysql> update emp set ename='RNG' where ename like 'rnf';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| KingFan | 2018-10-23 | 2000.00 |      1 |
| RNG     | 2000-01-01 | 3000.00 |      2 |
| edg     | 2000-01-01 | 4000.00 |      1 |
+---------+------------+---------+--------+
3 rows in set (0.00 sec)

删除记录

语法：delete from 表名 where 条件；
注意：不加where条件是删除表中所有记录

delete from emp where ename='KingFan';

mysql> select * from emp;
+---------+------------+---------+--------+
| ename   | hiredate   | sal     | deptno |
+---------+------------+---------+--------+
| KingFan | 2018-10-23 | 2000.00 |      1 |
| RNG     | 2000-01-01 | 3000.00 |      2 |
| edg     | 2000-01-01 | 4000.00 |      1 |
+---------+------------+---------+--------+
3 rows in set (0.00 sec)

mysql> delete from emp where ename='KingFan';
Query OK, 1 row affected (0.01 sec)

mysql> select * from emp;
+-------+------------+---------+--------+
| ename | hiredate   | sal     | deptno |
+-------+------------+---------+--------+
| RNG   | 2000-01-01 | 3000.00 |      2 |
| edg   | 2000-01-01 | 4000.00 |      1 |
+-------+------------+---------+--------+
2 rows in set (0.00 sec)

查询记录select

查询所有记录

语法select * from 表名

select * from emp
mysql> select * from emp;
+-------+------------+---------+--------+
| ename | hiredate   | sal     | deptno |
+-------+------------+---------+--------+
| rng   | 1993-01-01 | 2000.00 |      1 |
| edg   | 1993-01-01 | 3000.00 |      2 |
+-------+------------+---------+--------+
2 rows in set (0.00 sec)

mysql>

按字段名和条件查询

mysql> select ename from emp where deptno=1;
+-------+
| ename |
+-------+
| rng   |
+-------+
1 row in set (0.00 sec)

mysql>