时间：2014年3月27日20:08:01网站建表实战与优化意识
建表：
SNS社交网站：
会员表：member
Mysql中没有布尔型，相当于tinyint类型 false 就是0 其他都是true
大小 字节 |
列名称 |
列类型 |
默认值 |
是否主键 |
4 |
编号id |
int |
Primary key |
|
用户名：uesrname |
varchar(20) char(20) |
‘’ |
||
1 |
性别：gender |
char(1) tinyint |
||
1 |
体重KG：weight |
tinyint unsigned 0--255 |
||
3 |
生日：birthday |
date |
||
8 |
工资：salary |
Decimal(8,2) |
||
8 |
上次登录时间：lastlogin |
Datetime int |
||
个人简介intro |
Varchar(1500) |
|||
日志 blog |
text |
数据每一行的长度，都是固定的，查找的速度更快
浪费一定空间，从而加快速度值，但不能浪费过大
存储空间和时间时矛盾的的
时间换空间 空间换时间
所以intro 可以单独拿出来，另放到一张表里
大小 字节 |
列名称 |
列类型 |
默认值 |
是否主键 |
4 |
编号id |
int |
Primary key |
|
用户名：uesrname |
varchar(20) char(20) |
‘’ |
||
个人简介intro |
Varchar(1500) |
在开发中，会员的信息优化，把频繁用到的信息，优先考虑效率，存储到一张表中，
不常用的信息，或比较占据空间的信息，优先考虑空间占据，存储到辅表中
上次登录时间，从查询角度和计算来看，利用int时间戳进行计算
建表语法：所谓建表就是声明列的过程
create table 表名(
列1声明 列1参数,
列1声明 列1参数,
... ...
列n声明 列n参数
)engine myisam/innodb/bdb charset utf8/gbk/latin1;
create table member(
id int unsigned auto_increment primary key,
username char(20) not null default '',
gender char(1) not null default '',
weight tinyint unsigned not null default 0,
birthday date not null default '0000-00-00',
salary decimal(8,2) not null default 0
)engine myisam charset utf8;
时间：2014年3月28日17:11:02表修改语法之列的增删改
mysql> #修改表的语法：
mysql> #一张表，创建完毕，有了N个列
mysql> #之后还有可能增加或者删除列
mysql> #使用语句：
mysql> #alter table 表名 add 列名 列类型 列参数
mysql> use test;
Database changed
mysql> create table m1(
-> id int unsigned auto_increment primary key
-> )engine myisam charset utf8;
Query OK, 0 rows affected (0.08 sec)
mysql> desc m1;
+-------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
+-------+------------------+------+-----+---------+----------------+
1 row in set (0.05 sec)
mysql> alter table m1 add username char(20) not null default '';
Query OK, 0 rows affected (0.07 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
+----------+------------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
mysql> #关键熟悉列类型
mysql> alter table m1 birthday date not null default '0000-00-00';
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'birthday date not null default '0000-00-00'' at line 1
mysql> alter table m1 add birthday date not null default '0000-00-00';
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
3 rows in set (0.01 sec)
mysql> #发现gender性别列忘了加上，想加到username后，
mysql> alter table m1 add gender char(1) not null default '男' after username;
ERROR 1067 (42000): Invalid default value for 'gender'
mysql> set names gbk;
Query OK, 0 rows affected (0.02 sec)
mysql> alter table m1 add gender char(1) not null default '男' after username;
Query OK, 0 rows affected (0.08 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| gender | char(1) | NO | | 男 | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
4 rows in set (0.02 sec)
mysql> #在指定的列后，需要使用after
mysql> #如果想放到第一位，id前面
mysql> #用first
mysql> #alter table m1 add pid int not null default 0 first;
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| gender | char(1) | NO | | 男 | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
4 rows in set (0.01 sec)
mysql> alter table m1 add pid int not null default 0 first;
Query OK, 0 rows affected (0.06 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| pid | int(11) | NO | | 0 | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| gender | char(1) | NO | | 男 | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
5 rows in set (0.01 sec)
mysql> #把新列加到最前面，使用frist
mysql> #删除列，
mysql> alter table m1 drop pid;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| gender | char(1) | NO | | 男 | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
4 rows in set (0.01 sec)
mysql> #修改列
mysql> alter table m1 modify gender char(4) not null default '';
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| username | char(20) | NO | | | |
| gender | char(4) | NO | | | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+----------------+
4 rows in set (0.01 sec)
mysql> #modify 不能修改列名，
mysql> #修改列名和列类型，需要使用change
mysql> alter table m1 change id uid int unsigned;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+-------+
| uid | int(10) unsigned | NO | PRI | 0 | |
| username | char(20) | NO | | | |
| gender | char(4) | NO | | | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+-------+
4 rows in set (0.01 sec)
mysql> #主键在，自增长丢失
mysql> 如果列类型改变，导致数据存不下怎么办？
-> #主键在，自增长丢失
->
-> exit
-> ;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '如果列类型改变，导致数据存不下怎么办？
exit' at line 1
mysql> #主键在，自增长丢失
mysql> #如果列类型改变，导致数据存不下怎么办？
mysql> #比如，int改为smallint ，如果不匹配，数据将会丢失
mysql> #或者在mysql的strict mode下，修改不了
mysql> alter table m1 modify gender char(1) not null default '';
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc m1;
+----------+------------------+------+-----+------------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+------------+-------+
| uid | int(10) unsigned | NO | PRI | 0 | |
| username | char(20) | NO | | | |
| gender | char(1) | NO | | | |
| birthday | date | NO | | 0000-00-00 | |
+----------+------------------+------+-----+------------+-------+
4 rows in set (0.01 sec)
mysql> web操作的读写比是20:1
-> exit;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'web操作的读写比是20:1
exit' at line 1