企业如何给MYSQL创建表，查询表，创建索引实例
创建表
数据类型 int（整形，整数） not null，char（字符） tinyint（最小的整形） varchar （变长的字符类型）
create table xiaohu(
id int(4) not null,
name char(20) not null,
age tinyint(2) not null default '0',（不可以为空，但可以给0）
dept varchar(16) default null (可以为空)
如
mysql> create table student(
-> id int(4) not null,
-> name char(20) not null,
-> age tinyint(20) not null default '0',
-> dept varchar(16) default null
-> );
Query OK, 0 rows affected (0.01 sec)
查看见过表的语句：
show create table 表名\G；
mysql> show create table student\G;
*************************** 1. row ***************************
Table: student
Create Table: CREATE TABLE `student` (
`id` int(4) NOT NULL,
`name` char(20) NOT NULL,
`age` tinyint(20) NOT NULL DEFAULT '0',
`dept` varchar(16) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
查看表结构
desc 加表名
mysql> desc student;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(4) | NO | | NULL | |
| name | char(20) | NO | | NULL | |
| age | tinyint(20) | NO | | 0 | |
| dept | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
创建索引 提升查询速度
索引分类：
主键索引 主键列所有内容必须唯一 比如学号，准考证号
mysql> create table student(id int(4) not null AUTO_INCREMENT,递增 name char(20) not null, age tinyint(2) not null default '0', dept varchar(16) default null, primary key(id),主键索引 key index_name (name)普通索引 );
Query OK, 0 rows affected (0.01 sec)
如果在创建表的时候忘记加索引怎么办？
可以添加 语法
mysql> alter table student change id id int primary key auto_increment;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student
-> ;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | | NULL | |
| age | tinyint(2) | NO | | 0 | |
| dept | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
普通索引：
mysql> alter table student add index index_name(name); 改表 表的名字 添加 索引 索引名字（在哪个列上添加）
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc student;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | char(20) | NO | MUL | NULL | |
| age | tinyint(2) | NO | | 0 | |
| dept | varchar(16) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
指定前N个字符创建索引
mysql> create index index_dept on student(dept(8)); 创建 索引 索引名 在 表（第几个列（前几个字符））
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
查看索引 详细
mysql> show index from 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:
*************************** 2. row ***************************
Table: student
Non_unique: 1
Key_name: index_name
Seq_in_index: 1
Column_name: name
Collation: A
Cardinality: NULL
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
*************************** 3. row ***************************
Table: student
Non_unique: 1
Key_name: index_x
Seq_in_index: 1
Column_name: age
Collation: A
Cardinality: NULL
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
*************************** 4. row ***************************
Table: student
Non_unique: 1
Key_name: index_dept
Seq_in_index: 1
Column_name: dept
Collation: A
Cardinality: NULL
Sub_part: 8
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
4 rows in set (0.00 sec)
联合索引语法
create index index_name_dept on student(name,dept);
Table: student
Non_unique: 1
Key_name: ind_name_dept
Seq_in_index: 2
Column_name: dept
Collation: A
Cardinality: NULL
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
6 rows in set (0.00 sec)
mysql> drop index ind_name_dept on student; 删除索引 索引名 在 哪个表
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
创建联合索引前几个字符创建索引
create index ind_name_dept on student(name(8),dept(10));
到底给那些数据创建索引呢？
索引占空间，更新数据库还需要维护索引数据 写频繁读取好的语句少建立索引 十到几百行的小表不用创建索引
尽量在唯一值多的大表上建立索引
运维就是开个慢查询的语句开个监控