Mysql中对表字段的增删改查
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; +---------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+-------------+------+-----+---------+-------+ | ne_id | int(10) | YES | | NULL | | | ne_name | varchar(20) | 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; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ne_id | int(10) | YES | | NULL | | | ne_name | varchar(20) | YES | | NULL | | | ne_age | int(12) | YES | | NULL | | | ne_address | varchar(20) | 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; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ne_nor | int(10) | YES | | NULL | | | ne_name | varchar(20) | YES | | NULL | | | ne_age | int(12) | YES | | NULL | | | ne_address | varchar(20) | 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; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ne_name | varchar(20) | YES | | NULL | | | ne_age | int(12) | YES | | NULL | | | ne_address | varchar(20) | 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; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ne_name | varchar(20) | YES | | NULL | | | ne_age | varchar(20) | YES | | NULL | | | ne_address | varchar(20) | YES | | NULL | | +------------+-------------+------+-----+---------+-------+ 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; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | ne_nam