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: 0mysql> 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_normysql> alter table new change ne_id ne_nor int(10);query ok, 0 rows affected (0.22 sec)records: 0 duplicates: 0 warnings: 0mysql> 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: 0mysql> 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 varcharmysql> alter table new modify ne_age varchar(20);query ok, 0 rows affected (1.34 sec)records: 0 duplicates: 0 warnings: 0mysql> 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: 0mysql> desc new;+------------+-------------+------+-----+---------+-------+| field | type | null | key | default | extra |+------------+-------------+------+-----+---------+-------+| ne_name | varchar(20) | yes | | null | || ne_address | varchar(20) | yes | | null | || ne_age | varchar(20) | yes | | null | |+------------+-------------+------+-----+---------+-------+3 rows in set (0.00 sec)
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