Mysql中对表字段的增删改查

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mysql中对表字段的增加，修改（修改类型)，删除，排序

1.建立一个new 表，表中字段：学号，姓名，年龄。

mysql> create table new (ne_id int(10),ne_name varchar(20),ne_age int(12));

Query OK, 0 rows affected (0.97 sec)

2.表的结构图

mysql> desc new;

+---------+-------------+------+-----+---------+-------+

+---------+-------------+------+-----+---------+-------+

| ne_id | int(10) | YES | | NULL | |

| ne_age | int(12) | YES | | NULL | |

+---------+-------------+------+-----+---------+-------+

rows in set (0.01 sec)

3.向new 表中添加一个地址

mysql> alter table new add ne_address varchar(20);

Query OK, 0 rows affected (1.28 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc new;

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

| ne_id | int(10) | YES | | NULL | |

| ne_age | int(12) | YES | | NULL | |

+------------+-------------+------+-----+---------+-------+

rows in set (0.00 sec)

4.将字段名ne_id 改名为 ne_nor

mysql> alter table new change ne_id ne_nor int(10);

Query OK, 0 rows affected (0.22 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc new;

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

| ne_nor | int(10) | YES | | NULL | |

| ne_age | int(12) | YES | | NULL | |

+------------+-------------+------+-----+---------+-------+

4 rows in set (0.00 sec)

5.删除字段ne_nor

mysql> alter table new drop ne_nor;

Query OK, 0 rows affected (1.04 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc new;

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

| ne_age | int(12) | YES | | NULL | |

+------------+-------------+------+-----+---------+-------+

3 rows in set (0.00 sec)

6.修改字段类型：将ne_age 的 int 改为 varchar

mysql> alter table new modify ne_age varchar(20);

Query OK, 0 rows affected (1.34 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc new;

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

3 rows in set (0.01 sec)

7.排序

mysql> alter table new modify ne_age varchar(20) after ne_address;

Query OK, 0 rows affected (0.98 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> desc new;

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

+------------+-------------+------+-----+---------+-------+

3 rows in set (0.00 sec)