MySQL增删查改语句（入门）

目录

• create
• alter:
• insert
• delete
• update
• select

数据库定义语句:

1. create:创建数据库及表对象
2. drop:删除数据库及表对象
3. alter:修改数据库及表对象

数据库控制语句:

1. insert:向表中插入数据
2. delete:将表中数据删除
3. update:更改表中数据
4. select:检索表中数据

数据库管理语句:

1. grant:给用户授权
2. revoke:回收用户权限

create

mysql> create table customers
    -> (
    -> cust_id int(4) primary key not null auto_increment,  #创建表格,指定了主键,不允许为空,自增张
    -> cust_name char(20) not null,  
    -> cust_sex char(5) not null,
    -> cust_add char(20) not null default 'china',  #默认值为'China'
    -> cust_city char(20) not null default 'beijing'
    -> );

alter:

1. MariaDB [test]> alter table test.customers
    -> change column cust_sex sex char(2) null default 'M';
    //修改表中字段名称及数据类型，change子句。

2. MariaDB [test]> alter table test.customers
    -> alter column cust_city set default 'hangzhou';
    //alter子句用来修改表中字段的默认值的。
    
3. MariaDB [test]> alter table test.customers
    -> modify column cust_name char(20) first;
    //modify子句用来修改表中字段的数据类型，first表示将这个字段设为第一列。
    
4. MariaDB [test]> alter table test.customers
    -> drop column sex;
    //drop子句用来删除表中字段（列，一个意思，别混淆）

MariaDB [test]> desc test.customers;
+--------------+-------------+------+-----+----------+----------------+
| Field        | Type        | Null | Key | Default  | Extra          |
+--------------+-------------+------+-----+----------+----------------+
| cust_name    | char(20)    | YES  |     | NULL     |                |
| cust_id      | int(11)     | NO   | PRI | NULL     | auto_increment |
| cust_add     | varchar(50) | NO   |     | fd       |                |
| cust_city    | char(10)    | NO   |     | hangzhou |                |
| cust_contact | char(50)    | NO   |     | NULL     |                |
+--------------+-------------+------+-----+----------+----------------+

5. MariaDB [test]> alter table test.customers
    -> rename to test.customers_backup;
    MariaDB [test]> rename table test.customers_backup to test.customers;
    //rename子句用来修改表的名称
    
6. MariaDB [test]> show tables from test;
   //查看test库下表
   
7. MariaDB [test]> show columns from test.customers;
   //查看该表的字段以及数据类型

insert

MariaDB [(none)]> insert into
    -> test.customers 
    -> values
    -> ('zhangsan',101,'qiao','BeiJing','Ali');
	//向表中插入数据，千万要注意符合设定的约束即数据类型，字符要加引号。

MariaDB [(none)]> insert into test.customers
    -> set cust_name='111',cust_add='WU';
	//插入单个或多个指定字段的数据。

还有一个用法就是，insert……select，将从某个表对象查询的表插入到这个表对象中，需要注意的是，要注意数据类型一致性

delete

MariaDB [(none)]> delete from test.customers 
    -> where cust_name='lisi';
    //删除满足条件的行记录

update

MariaDB [(none)]> update test.customers
    -> set cust_add='ShanTou'
    -> where cust_name='zhangsan';

select

MariaDB [(none)]> select cust_name from test.customers where cust_name='qiao1';
	//查询指定字段，并满足where子句的条件。

MariaDB [(none)]> select cust_name,cust_add as dizhi from test.customers;
+-----------+-------+
| cust_name | dizhi |
+-----------+-------+
| qiao1     | BJ    |
| qiao2     | CD    |
+-----------+-------+
//as后起一个别名，并不改变表中数据

MariaDB [(none)]> select cust_name, case when cust_add='BJ' then 'BeiJing' else 'other city' end as dizhi from test.customers;
+-----------+------------+
| cust_name | dizhi      |
+-----------+------------+
| qiao1     | BeiJing    |
| qiao2     | other city |
+-----------+------------+


MariaDB [(none)]> select cust_name,cust_id+1000000000000000000000000000000 from test.customers;
+-----------+-----------------------------------------+
| cust_name | cust_id+1000000000000000000000000000000 |
+-----------+-----------------------------------------+
| qiao1     |         1000000000000000000000000000111 |
| qiao2     |         1000000000000000000000000000112 |
+-----------+-----------------------------------------+