我要评论首先创建一个数据库：
create database ku;
query ok, 1 row affected
查看一下是否有此数据库：
show databases;
+--------------------+
| database |
+--------------------+
| information_schema |
| ku |
| mysql |
| performance_schema |
| test |
+--------------------+
5 rows in set
使用此数据库：
use ku;
database changed
创建数据表：
create table biao(
name varchar(20),
age int(11),
sex char(11),
love varchar(11)
);
query ok, 0 rows affected
查看表结构：
desc biao;
+-------+-------------+------+-----+---------+-------+
| field | type | null | key | default | extra |
+-------+-------------+------+-----+---------+-------+
| name | varchar(20) | yes | | null | |
| age | int(11) | yes | | null | |
| sex | char(11) | yes | | null | |
| love | varchar(11) | yes | | null | |
+-------+-------------+------+-----+---------+-------+
4 rows in set
修改表名：
alter table biao rename biao1;
query ok, 0 rows affected
修改字段和类型：
alter table biao1 change sex sex1 char(20);
query ok, 0 rows affected
records: 0 duplicates: 0 warnings: 0
用圆括号！！！！
再查看一边：
desc biao1;
+-------+-------------+------+-----+---------+-------+
| field | type | null | key | default | extra |
+-------+-------------+------+-----+---------+-------+
| name | varchar(20) | yes | | null | |
| age | int(11) | yes | | null | |
| sex1 | char(20) | yes | | null | |
| love | varchar(11) | yes | | null | |
+-------+-------------+------+-----+---------+-------+
4 rows in set
修改字段的排列位置：
alter table biao1 modify name varchar(20) after sex1;
query ok, 0 rows affected
records: 0 duplicates: 0 warnings: 0
查看：
desc biao1;
+-------+-------------+------+-----+---------+-------+
| field | type | null | key | default | extra |
+-------+-------------+------+-----+---------+-------+
| age | int(11) | yes | | null | |
| sex1 | char(20) | yes | | null | |
| name | varchar(20) | yes | | null | |
| love | varchar(11) | yes | | null | |
+-------+-------------+------+-----+---------+-------+
4 rows in set
注意改的是大写出现的也是大写
加一个think字段：
alter table biao1 add think varchar (10) after love;
query ok, 0 rows affected
records: 0 duplicates: 0 warnings: 0
查看：
desc biao1;
+-------+-------------+------+-----+---------+-------+
| field | type | null | key | default | extra |
+-------+-------------+------+-----+---------+-------+
| age | int(11) | yes | | null | |
| sex1 | char(20) | yes | | null | |
| name | varchar(20) | yes | | null | |
| love | varchar(11) | yes | | null | |
| think | varchar(10) | yes | | null | |
+-------+-------------+------+-----+---------+-------+
5 rows in set
删除think：
alter table biao1 drop think;
query ok, 0 rows affected
records: 0 duplicates: 0 warnings: 0
查看：
desc biao1;
+-------+-------------+------+-----+---------+-------+
| field | type | null | key | default | extra |
+-------+-------------+------+-----+---------+-------+
| age | int(11) | yes | | null | |
| sex1 | char(20) | yes | | null | |
| name | varchar(20) | yes | | null | |
| love | varchar(11) | yes | | null | |
+-------+-------------+------+-----+---------+-------+
4 rows in set
删除此表：
drop table biao1;
query ok, 0 rows affected
查看：
show tables;
empty set
删除数据库：
drop database ku;
query ok, 0 rows affected
查看：
show databases;
+--------------------+
| database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set
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