資料，資料，命根就在資料 ! 操作資料庫時，一定要謹慎小心。師萬物 的程式碼看看就好，要有自己的判斷。遇到抉擇，要不恥上下問。

example

stu@Ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 85
Server version: 8.0.12 MySQL Community Server - GPL

Copyright (c) 2000, 2018, 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           |
 

+--------------------+
| db_herbal_medicine |
| employees          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.00 sec)

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

mysql> show warnings;
+-------+------+-------------------------------------------------------------+
| Level | Code | Message                                                     |
+-------+------+-------------------------------------------------------------+
| Note  | 1007 | Can'
 
t create database 'db_herbal_medicine'; database exists |
+-------+------+-------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> exit
Bye
stu@Ubuntu:~$ 

more knowledge

• 在[2]中提到的：注意：warnings只記錄上一次執行的提示，如果你在出現一個warning之後，再執行了一次正常的查詢，如select 1/0; 得到一個warning,然後又執行了select now();這次沒有告警，你再做show warnings也是看不到告警資訊了。
• 基於MySQL8，測試結果如下所示。

stu@Ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 86
Server version: 8.0.12 MySQL Community Server - GPL

Copyright (c) 2000, 2018, 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> create database if not exists db_herbal_medicine;
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select now();
+---------------------+
| now()               |
+---------------------+
| 2018-10-21 20:40:22 |
+---------------------+
1 row in set (0.00 sec)

mysql> show warnings;
Empty set (0.00 sec)

mysql> exit
Bye
stu@Ubuntu:~$ 

reference

resource

MySQL是一個關係型資料庫管理系統，目前是開源的(2018-10)。
許可權明確，引擎與字符集等選擇恰當，命名規範。
MariaDB，Redis，MongoDB，PostgreSQL，Hive，HBase等，多作了解，拓寬心量。
Workbench，phpMyAdmin，Navicat等圖形化管理工具，豫兮若冬涉川。