MySQL之创建库
刘宇帅MySQL 创建库语法
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
[create_specification] ...
create_specification:
[DEFAULT] CHARACTER SET [=] charset_name
| [DEFAULT] COLLATE [=] collation_name创建一个默认的数据库
create database school;执行结果
mysql> create database school;
Query OK, 1 row affected (0.03 sec)查看数据库创建情况
mysql> show create database school;
+----------+-----------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------------------------------------+
| school | CREATE DATABASE `school` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */ |
+----------+-----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)如上语法中创建数据库可以使用 database 也可以使用 schema，使用 schema 并和上面做下对比
mysql> create schema school;
Query OK, 1 row affected (0.00 sec)
mysql> show create database school;
+----------+-----------------------------------------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------------------------------------+
| school | CREATE DATABASE `school` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci */ |
+----------+-----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)创建数据库语法中有一句if not exists用来检查数据是否存在，当不存在的时候才会创建，再次执行创建语句如下
mysql> create database school;
ERROR 1007 (HY000): Can't create database 'school'; database exists
mysql> create database if not exists school;
Query OK, 1 row affected, 1 warning (0.00 sec)当我们直接创建的话会直接报错，用 if not exists 就不会，当我们要导入库和表到库里的时候可以加上这句避免 sql 执行一半就停掉等。
字符集 和 字符序
Mysql 提供不同的字符集支持数据字符和字符编码，另外提供了字符序来进行数据比较。
举例：字符 A、a、B、b的编码分别为 0、1、2、3，当进行字符比较的时候 0 < 2所有 A < B,而当比较 A、a 的时候虽然 0 < 1 但是 A = a。
字符序 和 字符集关系
一个字符集至少对应一个字符序
两个不同的字符集不能有相同的字符序。
每个字符集都有默认的字符序。
MySQL 提供了四种级别的字符集和字符序的设置，包括 server级、database级、table级、column级，我们可以在任何级别来设置字符集和字符序。
查看 MySQL 支持的字符集
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 |
| utf16le | UTF-16LE Unicode | utf16le_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 |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci | 4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.01 sec)其他的查询方式之 information_schema
mysql> use information_schema;
Database changed
mysql> select * from CHARACTER_SETS;
+--------------------+----------------------+---------------------------------+--------+
| CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION | MAXLEN |
+--------------------+----------------------+---------------------------------+--------+
| big5 | big5_chinese_ci | Big5 Traditional Chinese | 2 |
| dec8 | dec8_swedish_ci | DEC West European | 1 |
| cp850 | cp850_general_ci | DOS West European | 1 |
| hp8 | hp8_english_ci | HP West European | 1 |
| koi8r | koi8r_general_ci | KOI8-R Relcom Russian | 1 |
| latin1 | latin1_swedish_ci | cp1252 West European | 1 |
......
......直接全局查询
mysql> show character set where charset='utf8';
+---------+---------------+-------------------+--------+
| Charset | Description | Default collation | Maxlen |
+---------+---------------+-------------------+--------+
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
+---------+---------------+-------------------+--------+
1 row in set (0.00 sec)
mysql> show character set where charset like 'utf8%';
+---------+---------------+--------------------+--------+
| Charset | Description | Default collation | Maxlen |
+---------+---------------+--------------------+--------+
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
+---------+---------------+--------------------+--------+
2 rows in set (0.00 sec)查看 MySQL 支持的字符序
mysql> SHOW COLLATION;
+--------------------------+----------+-----+---------+----------+---------+
| Collation | Charset | Id | Default | Compiled | Sortlen |
+--------------------------+----------+-----+---------+----------+---------+
| big5_chinese_ci | big5 | 1 | Yes | Yes | 1 |
| big5_bin | big5 | 84 | | Yes | 1 |
| dec8_swedish_ci | dec8 | 3 | Yes | Yes | 1 |
| dec8_bin | dec8 | 69 | | Yes | 1 |
| cp850_general_ci | cp850 | 4 | Yes | Yes | 1 |
| cp850_bin | cp850 | 80 | | Yes | 1 |
| hp8_english_ci | hp8 | 6 | Yes | Yes | 1 |
| hp8_bin | hp8 | 72 | | Yes | 1 |
| koi8r_general_ci | koi8r | 7 | Yes | Yes | 1 |
| koi8r_bin | koi8r | 74 | | Yes | 1 |
.........
.........其他查询之 information_schema
mysql> USE information_schema;
mysql> SELECT * FROM COLLATIONS字符序命名是以字符集为前缀命名的，例如 utf8_general_ci 是 utf8 的字符序。
创建指定字符序 和 字符集的 database
mysql> create database if not exists school character set 'utf8' collate 'utf8_general_ci';
Query OK, 1 row affected (0.00 sec)
mysql> show create database school;
+----------+-----------------------------------------------------------------+
| Database | Create Database |
+----------+-----------------------------------------------------------------+
| school | CREATE DATABASE `school` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select @@character_set_database,@@collation_database;
+--------------------------+----------------------+
| @@character_set_database | @@collation_database |
+--------------------------+----------------------+
| utf8 | utf8_general_ci |
+--------------------------+----------------------+
1 row in set (0.00 sec)删除数据库
mysql> drop database school;
Query OK, 0 rows affected (0.01 sec)库创建实践
我们在实践中建库使用 utf8mb4 编码，如下
mysql> create database if not exists school character set 'utf8mb4' collate 'utf8mb4_general_ci';
Query OK, 1 row affected (0.00 sec)
mysql> show create database school;
+----------+--------------------------------------------------------------------+
| Database | Create Database |
+----------+--------------------------------------------------------------------+
| school | CREATE DATABASE `school` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+--------------------------------------------------------------------+
1 row in set (0.00 sec)刘宇帅
非著名程序员，全栈开发工程师，长期专注系统开发与架构设计。
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