MySQL-5.7創建及查看數據庫

1.創建數據庫語句
create database語句是在MySQL實例上創建一個指定名稱的數據庫。
create schema語句的語義和create database是一樣的。

2.語法解析

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
    [create_specification] ...

create_specification:
    [DEFAULT] CHARACTER SET [=] charset_name
  | [DEFAULT] COLLATE [=] collation_name

（1）用給定的名稱創建數據庫。如果用這句話，你需要創建數據庫的權限。創建模式是一個創建數據庫的同義詞。
（2）如果數據庫存在且未指定是否存在，則會出現錯誤。
（3）在一個活躍的鎖表語句的會話中不允許創建數據庫。
（4）create_specification選項指定創建數據庫的屬性，並存儲在數據庫目錄的db.opt文件中。

• charcter set屬性指定數據庫的默認字符集；
• collate屬性指定此數據庫的默認排序規則。

[root@localhost course]# ls
course.frm  course.ibd  db.opt  dept.frm  dept.ibd  students.frm  students.ibd  teacher_backup.frm  teacher_backup.ibd  teacher.frm  teacher.ibd
[root@localhost course]# cat db.opt 
default-character-set=latin1
default-collation=latin1_swedish_ci

（5）MySQL中的數據庫被實現為一個目錄，該目錄包含與數據庫中的表相對應的文件。因為當數據庫初始化時是沒有表的，創建數據庫語句只在MySQL數據目錄下創建一個目錄的和db.opt文件。
（6）如果在數據庫目錄下手動創建目錄（使用mkdir），服務器認為它是數據庫目錄，並顯示在數據庫里。
（7）你也可以使用mysqladmin程序創建數據庫。

3.實踐演示

mysql> create database test2;
Query OK, 1 row affected (0.00 sec)

mysql> show create database test2;
+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| test2    | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> create database test3 character set utf8;
Query OK, 1 row affected (0.00 sec)

mysql> show create database test3;
+----------+----------------------------------------------------------------+
| Database | Create Database                                                |
+----------+----------------------------------------------------------------+
| test3    | CREATE DATABASE `test3` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> create database test3;
ERROR 1007 (HY000): Can't create database 'test3'; database exists
mysql> create database if not exists test3;
Query OK, 1 row affected, 1 warning (0.00 sec)

4.創建數據庫的另一種方式

[root@localhost data]# pwd
/data1/mysql/data
[root@localhost data]# mkdir test1
[root@localhost data]# chown mysql:mysql -R test1
[root@localhost data]# mysql -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.7.20 MySQL Community Server (GPL)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| a1                 |
| a2                 |
| a3                 |
| course             |
| mysql              |
| performance_schema |
| sys                |
| test1              |
+--------------------+
9 rows in set (0.01 sec)

5.查看數據庫創建語句

SHOW CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name

顯示創建命名數據庫的創建數據庫語句。
如果顯示語句包含"IF NOT EXISTS"子句，輸出也包含這樣一個子句。"SHOW CREATE SCHEMA"是"SHOW CREATE DATABASE"的同義詞。

mysql> show create database test2\G
*************************** 1. row ***************************
       Database: test2
Create Database: CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET latin1 */
1 row in set (0.00 sec)

mysql> show create database test2;
+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| test2    | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create schema test2;
+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| test2    | CREATE DATABASE `test2` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+
1 row in set (0.00 sec)