mysql基础 create database if not exists... 若数据库不存在则创建

•        OS : Ubuntu 18.04.1 LTS
•        DBMS : mysql 8.0.12

示例

stu@Ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 91
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 (0.01 sec)

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> drop database db_herbal_medicine;
Query OK, 0 rows affected (0.01 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| employees          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> create database if not exists db_herbal_medicine;
Query OK, 1 row affected (0.04 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| db_herbal_medicine |
| employees          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
6 rows in set (0.00 sec)

mysql> exit
Bye
stu@Ubuntu:~$ 

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