1.Mysql 创建数据库
(1)创建一个新数据库Mysqltest
MariaDB [lijw]> show databases;
MariaDB [lijw]> create databases Mysqltest;
(2) 创建一个数据库测试表lijw_test
查看刚刚创建数据库Mysqltest
MariaDB [lijw]> use Mysqltest;
MariaDB [Mysqltest]> show tables;
刚刚创建的数据库Mysqltest中无任何表
创建测试表
MariaDB [Mysqltest]> create table lijw_test(id smallint unsigned auto_increment primary key,
username varchar(20),
account int(64) not null,
password varchar(64) not null);
MariaDB [Mysqltest]> show tables;
查看表字段:
MariaDB [Mysqltest]> show columns from lijw_test;
修改lijw_test字段,将username columns字段修改为default not null:
MariaDB [Mysqltest]> ALTER TABLE lijw_test MODIFY username VARCHAR(20) NOT NULL;
MariaDB [Mysqltest]> insert into lijw_test(username,account,password)values('lijw','tangjihede','a1868676219');
由于类型不对导致,account value值没有插入,由于account为int类型 not null ,所以default 0
修改account字符类型:
MariaDB [Mysqltest]> ALTER TABLE lijw_test account varchar(64) not null;
MariaDB [Mysqltest]> insert into lijw_test(username,account,password)values('lijw','tangjihede','a1868676219');
删除插入错误的数据:
MariaDB [Mysqltest]> delete from lijw_test where account = '0';
MariaDB [Mysqltest]> select * from lijw_test;
修改lijw_test表数据:
MariaDB [Mysqltest]> update lijw_test set password = 'a18686762192' where username = 'lijw';
基础知识,创建数据库,创建表,Mysql数据库简单的增删改查