mysql修改表

页面导航:首页 > 数据库 > Mysql > mysql修改表

mysql修改表

来源: 作者: 时间:2016-01-30 09:02 【

修改表结构:alter [ignore] table table specification table structure changetable structure change 包括表属性改变,列属性改变,完整性约束改变。1 表属性改变1 1重命名表名mysql
修改表结构:
alter [ignore] table <table specification> <table structure change>

<table structure change> 包括表属性改变,列属性改变,完整性约束改变。

1.表属性改变

1.1重命名表名

> alter table student rename to s;
Query OK, 0 rows affected (0.03 sec)
也可以直接使用rename命令改名:
mysql> rename table s to student;
Query OK, 0 rows affected (0.13 sec) 

1.2表排序改变

mysql> alter table student order by stu_id desc;
mysql> select * from student;
+--------+----------+---------+-----------+
| stu_id | stu_name | stu_tel | stu_score |
+--------+----------+---------+-----------+
|      4 | d        |     154 |        63 |
|      3 | c        |     153 |        62 |
|      2 | b        |     152 |        61 |
|      1 | a        |     151 |        60 |
+--------+----------+---------+-----------+

2列属性改变

2.1 添加列

mysql> alter table student
    -> add sex char(1) after stu_name;
Query OK, 4 rows affected (0.34 sec)
Records: 4  Duplicates: 0  Warnings: 0
mysql> select * from student;
+--------+----------+------+---------+-----------+
| stu_id | stu_name | sex  | stu_tel | stu_score |
+--------+----------+------+---------+-----------+
|      1 | a        | NULL |     151 |        60 |
|      2 | b        | NULL |     152 |        61 |
|      3 | c        | NULL |     153 |        62 |
|      4 | d        | NULL |     154 |        63 |
+--------+----------+------+---------+-----------+
4 rows in set (0.02 sec)
新添加的列默认放在最后一列,且默认填充空值。这里使用after指定了新增列sex放在stu_name后面.如果新增列设置不能为空,那么mysql将根据列的数据类型填入实际的值:对于数值填入0,对于字符串填入空字符串,对于日期填入0000-00-00,对于时间填入00:00:00.

2.2删除列

mysql> alter table student
    -> drop sex;
Query OK, 4 rows affected (0.33 sec)
Records: 4  Duplicates: 0  Warnings: 0

2.3修改列属性

初始列属性:
+-------------+-----------+
| column_name | data_type |
+-------------+-----------+
| stu_id      | int       |
| stu_name    | varchar   |
| stu_tel     | int       |
| stu_score   | int       |
+-------------+-----------+
将stu_tel列修改为tel char型,并放在stu_score后面。
mysql> alter table student
    -> change stu_tel tel char(3) after stu_score;;
Query OK, 4 rows affected (0.23 sec)
+-------------+-----------+
| column_name | data_type |
+-------------+-----------+
| stu_id      | int       |
| stu_name    | varchar   |
| stu_score   | int       |
| tel         | char      |
+-------------+-----------+
如果仅仅是更改列其他属性而不改列名时,可以使用modify参数。
将tel列改回int型
mysql> alter table student
    -> modify tel int(3);
Query OK, 4 rows affected (0.25 sec)
Records: 4  Duplicates: 0  Warnings: 0
+-------------+-----------+
| column_name | data_type |
+-------------+-----------+
| stu_id      | int       |
| stu_name    | varchar   |
| stu_score   | int       |
| tel         | int       |
+-------------+-----------+

3.完整性约束改变

<integrity constraint change>:=
add primary key<index name>
add unique <index name>
add foreign key <index name>(column list) referencing <specification>
add check <condition>
drop primary key
drop foreign key <index name>
drop constraint <constraint name>
在add后面可以添加[constraint <constraint name>] 为完整性约束定义名字。
删除主键:
mysql> alter table student drop primary key;
添加主键:
mysql> alter table student add primary key(stu_id);
Tags:

文章评论

最 近 更 新
热 点 排 行
Js与CSS工具
代码转换工具

<