mysql数据库/数据表的创建/查看

时间:2022-12-13 03:21:42

一: 创建数据库
方法一:

[root@host]# mysqladmin -u root -p create database1
Enter password:******

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| database1 |
| mysql |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)

方法二:

mysql> create database database2;
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| database1 |
| database2 |
| mysql |
| performance_schema |
+--------------------+
5 rows in set (0.00 sec)

二: 建立资料表
mysql> use database1;
Database changed
mysql> show tables;
Empty set (0.00 sec)

这时候需要你去决定你需要什么样的资料库资料表, 各个资料库资料表中有什么样的列.
(如果后期相对数据表格式进行修改, 增加列,删除列,修改列的名字之类的)
这个中间涉及到了mysql中数据类型的一些问题
http://www.runoob.com/mysql/mysql-data-types.html
其中name, owner, species我们使用的是VARCHAR变长字符串, 大小未0-65535个字节, sex使用的是单字节的定长字符串, birth, death使用的是DATE日期类型.

mysql> create table pet (name VARCHAR(20), owner VARCHAR(20), 
-> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);
Query OK, 0 rows affected (0.07 sec)
mysql> show tables;
+---------------------+
| Tables_in_database1 |
+---------------------+
| pet |
+---------------------+
1 row in set (0.00 sec)
mysql> describe pet; / desc pet;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| owner | varchar(20) | YES | | NULL | |
| species | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
| birth | date | YES | | NULL | |
| death | date | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

三: 填写数据表内容 (重点)
通过LOAD DATA和INSERT语句可以完成。
方法一: 直接load一个文本
(貌似还可以导入csv格式文件, 需要研究一下)
基本语法:

load data [low_priority | concurrent] [local] infile 'filename'
[REPLACE | IGNORE]
INTO TABLE tbl_name
[CHARACTER SET charset_name]
[{FIELDS | COLUMNS}
[TERMINATED BY 'string']
[[OPTIONALLY] ENCLOSED BY 'char']
[ESCAPED BY 'char']
]
[LINES
[STARTING BY 'string']
[TERMINATED BY 'string']
]
[IGNORE number {LINES | ROWS}]
[(col_name_or_user_var,...)]
[SET col_name = expr,...]

其中:
https://dev.mysql.com/doc/refman/5.5/en/load-data.html
(每个参数权威的解释在官方文件中, 这里直接是我理解的,有些我没用过/不理解的就不说了.)
在读取位于服务器上的文件时, 文件必须处于服务器目录或者是要有对文件的读取权限.
low_priority 没有用户在读这个文件的时候,执行load data.
local 表示从client host上面读文件, 如果local未指定, 则文件必须位于server host上面.
replace 输入行内容将代替已存在的行的内容.
ignore 遇到有唯一键值的行则跳过.
FIELDS | COLUMNS关键字:
terminated by描述字段的分隔符,默认情况下是tab字符(\t)
enclosed by描述的是字段的括起字符。
escaped by描述的转义字符。默认的是反斜杠(backslash:\ )
LINES关键字:
每条记录的分隔符默认为’\n’即为换行符.
这个版本默认的格式是每个数值之间用tab键隔开,然后每一组数据之间用enter键隔开, 没有数值的项用\N来表示(显示出来的就是NULL). 如下是我在txt文件中输入的结果:

Fluffy  Harold  cat f   1993-02-04  \N 
Claws Gwen cat m 1994-03-17 \N
Buffy Harold dog f 1989-05-13 \N
Fang Benny dog m 1990-08-27 \N
Bowser Diane dog m 1979-08-31 \N
Chirpy Gwen bird \N 1997-12-09 \N
Whistler Gwen bird \N 1997-12-09 \N
Slim Benny snake m 1996-04-29 \N

你也可以自己在后面定义自己觉得习惯的格式.
例如我这里想尝试用用””表示字段括起字符, 逗号表示字段分隔符, 换行符\表示每个记录的分隔符.

mysql>load data local infile '/path/Documents/pet.txt' into table pet fields terminated by ',' enclosed by ' '' ' lines terminated by '/n'; 

注意:
同时还遇到了一个问题:

mysql> load data local infile '/path/Documents/pet.txt' into table pet; 
ERROR 1148 (42000): The used command is not allowed with this MySQL version

貌似是个security issues:
https://*.com/questions/18437689/error-1148-the-used-command-is-not-allowed-with-this-mysql-version
https://*.com/questions/16285864/how-can-i-correct-mysql-load-error
只需要退出,再用如下命令登录就好了

mysql -u root -p --local-infile  **加上--local-infile**

查看导入结果:

mysql> load data local infile '/path/Documents/pet.txt' into table pet; 
Query OK, 8 rows affected (0.03 sec)
Records: 8 Deleted: 0 Skipped: 0 Warnings: 0
mysql> select * from pet;
+----------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Fang | Benny | dog | m | 1990-08-27 | NULL |
| Bowser | Diane | dog | m | 1979-08-31 | NULL |
| Chirpy | Gwen | bird | NULL | 1997-12-09 | NULL |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
| Slim | Benny | snake | m | 1996-04-29 | NULL |
+----------+--------+---------+------+------------+-------+
8 rows in set (0.00 sec)

方法二: 利用insert语句
上面是批量的导入数据的方法, 如果你希望一次导入一组或者一个新数据的话.(当然load data也是可以指定导入部分内容的)
最简单的形式是,提供每一列的值,其順序与CREATE TABLE语句中列的順序相同。假定Diane把一个新仓鼠命名为Puffball,可以使用下面的INSERT语句新增一条新纪录:

mysql> insert into pet 
-> values ('Puffball','Diane','hamster','f','1999-03-30',NULL);
Query OK, 1 row affected (0.09 sec)

mysql> select * from pet;
+----------+--------+---------+------+------------+-------+
| name | owner | species | sex | birth | death |
+----------+--------+---------+------+------------+-------+
| Fluffy | Harold | cat | f | 1993-02-04 | NULL |
| Claws | Gwen | cat | m | 1994-03-17 | NULL |
| Buffy | Harold | dog | f | 1989-05-13 | NULL |
| Fang | Benny | dog | m | 1990-08-27 | NULL |
| Bowser | Diane | dog | m | 1979-08-31 | NULL |
| Chirpy | Gwen | bird | NULL | 1997-12-09 | NULL |
| Whistler | Gwen | bird | NULL | 1997-12-09 | NULL |
| Slim | Benny | snake | m | 1996-04-29 | NULL |
| Puffball | Diane | hamster | f | 1999-03-30 | NULL |
+----------+--------+---------+------+------------+-------+
9 rows in set (0.01 sec)

注意:
这里字串和日期值均为引号括起来的字串。另外,可以直接用INSERT語句插入NULL表示资料表不存在的值。不能使用LOAD DATA中所示的的\N。