09.数据库的管理应用

9.1 创建数据库

命令语法：create database <数据库名> <==注意库名不能数字开头，大小写不敏感
在 MySQL 默认字符集情况下建立数据库测试如下：
建立一个名为 oldboy 的数据库
mysql> show databases like 'oldboy';
+-------------------+
| Database (oldboy) |
+-------------------+
| oldboy |
+-------------------+
1 row in set (0.04 sec)
查看建库的语句 (注意:如果编译时指定字符集是 utf8，创建数据库时默认指定是 utf8)
mysql> show create database oldboy;
+----------+-----------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------+
| oldboy | CREATE DATABASE `oldboy` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------------------+
1 row in set (0.00 sec)
创建一个指定字符集的数据库
mysql> create database oldboy_gbk CHARACTER SET gbk COLLATE gbk_chinese_ci;
Query OK, 1 row affected (0.00 sec)
mysql> show create database oldboy_gbk;
+------------+--------------------------------------------------------------------+
| Database | Create Database |
+------------+--------------------------------------------------------------------+
| oldboy_gbk | CREATE DATABASE `oldboy_gbk` /*!40100 DEFAULT CHARACTER SET gbk
*/ |
+------------+--------------------------------------------------------------------+
1 row in set (0.00 sec)

9.2 查询库的字符集及校队规则

mysql> SHOW CHARACTER SET；
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
+----------+-----------------------------+---------------------+--------+
39 rows in set (0.00 sec) 

9.3 企业场景创建什么字符集的数据库

1、根据开发的程序确定字符集（建议 UTF8）
2、可以编译的时候指定字符集，例如：
--DDEFAULT_CHARSET=utf8 
--DDEFAULT_COLLATION=utf8_general_ci 
然后建库的时候默认创建即可，create database oldboy；
3、编译的时候没有指定字符集或者指定了和程序不同的字符集，如何解决？
指定字符集创建数据库即可
例如：
create database oldboy_gbk DEFAULT CHARACTER SET gbk COLLATE gbk_chinese_ci <==
创建 gbk 字符集数据库

9.4 显示数据库

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| oldboy |
| oldboy_gbk |
| performance_schema |
+--------------------+
5 rows in set (0.05 sec)

9.5 删除数据库

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| oldboy |
| oldboy_gbk |
| performance_schema |
+--------------------+
5 rows in set (0.00 sec)
mysql> drop database oldboy;
Query OK, 0 rows affected (0.05 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| oldboy_gbk |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)

9.6 进入数据库中指定的库

mysql> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| mysql |
+------------+
1 row in set (0.00 sec)

9.7 查看进入当前数据库的用户

mysql> select user();
+----------------+
| user() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.05 sec)

9.8 删除数据库中多余的账号 

语法：drop user ‘user’@’主机域 0 ’ <--注意引号，可以是单或双引号，但是不能不加

mysql>drop user ‘root’@’oldboy’;
mysql>drop user ‘ ’@’localhost’; <--没有的部分就用两个单引号代替即可
如果 drop 删除不了（一般是特殊字符或大写），可以用下面方式删除（以 root 用户，oldboy
主机为例）
delete from mysql.user where user=’root’ and host=’oldboy’
flush privileges;​

9.9 查看数据库的用户

mysql> select user,host from mysql.user;
+------+-----------+
| user | host |
+------+-----------+
| root | 127.0.0.1 |
| root | localhost |
+------+-----------+
2 rows in set (0.06 sec)