mysql基础 show warnings 查看警告信息

原创云散月明 All China Database Union 2021-04-23

2240

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 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:~$

扩展

在[2]中提到的：注意：warnings只记录上一次执行的提示，如果你在出现一个warning之后，再执行了一次正常的查询，如select 1/0; 得到一个warning,然后又执行了select now();这次没有告警，你再做show warnings也是看不到告警信息了。
基于MySQL8，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 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:~$