[Spring Boot]运行报错“Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection;”

（之前运行都是好好的，突然运行项目出现问题，报错的是数据库相关，正好顺便整理一下数据库）
具体报错如下：

There was an unexpected error (type=Internal Server Error, status=500).
nested exception is org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. ### The error may exist in file [C:\Users\（项目路径）\UserMapper.xml] ### The error may involve com.house.mjxd.dao.UserMapper.login ### The error occurred while executing a query ### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

显然重点就是没连接上数据库，遂试图检查sqlyog连接数据库，发现连接也出了问题

解决此问题的方法是启动mysql服务，具体解决过程见这一篇，应该算踩坑集合了吧哈哈哈虽然很简单。

好吧，这篇没什么重要输出，就是说数据库连接问题报的错，解决数据库问题就运行正常了（项目没问题的前提下）