mysql基础 drop database if exists... 若数据库存在则删除

原创云散月明 All China Database Union 2021-04-26

2126

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 92
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> drop database if exists db_herbal_medicine;
Query OK, 0 rows affected (0.08 sec)

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

mysql> drop database if exists db_herbal_medicine;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> exit
Bye
stu@Ubuntu:~$

扩展

在[1]中提到的：“先通过drop database if exists aa试图删除一个不存在的数据库aa，系统出现提示1warning，此时通过show warnings查询显示的是empty set；”。
基于MySQL8进行测试，结果如下所示：

stu@Ubuntu:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 93
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           |
+--------------------+
| employees          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

mysql> drop database if exists db_herbal_medicine;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings;
Empty set (0.00 sec)

mysql> \W
Show warnings enabled.
mysql> drop database if exists db_herbal_medicine;
Query OK, 0 rows affected, 1 warning (0.00 sec)

Note (Code 1008): Can't drop database 'db_herbal_medicine'; database doesn't exist
mysql> \w
Show warnings disabled.
mysql> exit
Bye
stu@Ubuntu:~$