Linux学习笔记:MySQL创建表
内容导读
互联网集市收集整理的这篇技术教程文章主要介绍了Linux学习笔记:MySQL创建表,小编现在分享给大家,供广大互联网技能从业者学习和参考。文章包含6192字,纯文字阅读大概需要9分钟。
内容图文
![Linux学习笔记:MySQL创建表](/upload/InfoBanner/zyjiaocheng/460/867c783a23fe4e3db2671c7a0faffe1f.jpg)
语句
Create Table: CREATE TABLE `student` (
`id` int(4) NOT NULL,
`name` varchar(16) NOT NULL,
`score` int(1) DEFAULT ‘0‘
) ENGINE=InnoDB DEFAULT CHARSET=utf8
增加主键
alter table student change id id int primary key auto_increment ;
一般不需要修改主键,但有时建表的时候忘记了加,要后补就可以这样写
格式是alter table <表名> change <旧字段名> <新字段名> 字段属性,这里的auto_increment也是后补上去的。
mysql> desc mydb.student; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(16) | NO | | NULL | | | score | int(1) | YES | | 0 | | +-------+-------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec)
添加索引
mysql> alter table mydb.student add index name(name); Query OK, 0 rows affected (0.63 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc mydb.student; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(16) | NO | MUL | NULL | | | score | int(1) | YES | | 0 | | +-------+-------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec)
那个name(name)其实是索引名(字段名),索引名字可以自行定义。成功后,在desc里可以看到key显示MUL。
删除索引
alter table mydb.student drop index name;
这里的name是索引的名字
查看索引
show index from mydb.student; +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | student | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | | +---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 1 row in set (0.00 sec)
创建部分内容的索引
有些内容比较长,但其中前几个字符已经是唯一的情况下,即可使用这几个字符形成索引。
例如使用name的前4个字符形成索引
mysql> create index index_name on mydb.student (name(4)); Query OK, 0 rows affected (0.20 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc mydb.student; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(16) | NO | MUL | NULL | | | score | int(1) | YES | | 0 | | +-------+-------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) mysql> show index from mydb.student\G; *************************** 1. row *************************** Table: student Non_unique: 0 Key_name: PRIMARY Seq_in_index: 1 Column_name: id Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: Index_type: BTREE Comment: Index_comment: *************************** 2. row *************************** Table: student Non_unique: 1 Key_name: index_name Seq_in_index: 1 Column_name: name Collation: A Cardinality: 0 Sub_part: 4 Packed: NULL Null: Index_type: BTREE Comment: Index_comment: 2 rows in set (0.00 sec) ERROR: No query specified
看2. Row的Sub_part
关于索引类型,参考http://blog.sina.com.cn/s/blog_6fd335bb0100v1lm.html
创建联合索引
在上面索引的基础上,输入多个字段名用以创建一个联合索引
例如
mysql> create index index_id_name on mydb.student (id,name(4)); Query OK, 0 rows affected (0.13 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from mydb.student \G *************************** 1. row *************************** Table: student Non_unique: 0 Key_name: PRIMARY Seq_in_index: 1 Column_name: id Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: Index_type: BTREE Comment: Index_comment: *************************** 2. row *************************** Table: student Non_unique: 1 Key_name: index_name Seq_in_index: 1 Column_name: name Collation: A Cardinality: 0 Sub_part: 4 Packed: NULL Null: Index_type: BTREE Comment: Index_comment: *************************** 3. row *************************** Table: student Non_unique: 1 Key_name: index_id_name Seq_in_index: 1 Column_name: id Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: Index_type: BTREE Comment: Index_comment: *************************** 4. row *************************** Table: student Non_unique: 1 Key_name: index_id_name Seq_in_index: 2 Column_name: name Collation: A Cardinality: 0 Sub_part: 4 Packed: NULL Null: Index_type: BTREE Comment: Index_comment: 4 rows in set (0.00 sec) 可以看到第3、4行的key_name是一样的
删除联合索引也是一样用索引名字即可
mysql> drop index index_id_name on mydb.student; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0
创建单一索引,在关键字index前加unique关键字
mysql> create unique index index_id_name on mydb.student (id,name(4)); Query OK, 0 rows affected (0.23 sec) Records: 0 Duplicates: 0 Warnings: 0
Linux学习笔记:MySQL创建表
标签:mysql
本文系统来源:http://coosh.blog.51cto.com/6334375/1736239
内容总结
以上是互联网集市为您收集整理的Linux学习笔记:MySQL创建表全部内容,希望文章能够帮你解决Linux学习笔记:MySQL创建表所遇到的程序开发问题。 如果觉得互联网集市技术教程内容还不错,欢迎将互联网集市网站推荐给程序员好友。
内容备注
版权声明:本文内容由互联网用户自发贡献,该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 gblab@vip.qq.com 举报,一经查实,本站将立刻删除。
内容手机端
扫描二维码推送至手机访问。