前言

Maven项目连接MySql数据库，进行数据库操作时报如下问题:

java.sql.SQLException: Unknown system variable ‘query_cache_size’

报错信息如下

org.apache.ibatis.exceptions.PersistenceException: 
### Error updating database.  Cause: java.sql.SQLException: Unknown system variable 'query_cache_size'
### Cause: java.sql.SQLException: Unknown system variable 'query_cache_size'
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:200)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.insert(DefaultSqlSession.java:185)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:57)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
	at com.sun.proxy.$Proxy27.insert(Unknown Source)
	at com.nzc.ums.service.impl.UserServiceImpl.regist(UserServiceImpl.java:32)
	at com.nzc.ums.action.UserAction.doPost(UserAction.java:45)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

问题原因

查看pom.xml文件后发现，mysql驱动程序的版本为5.1.38，而我本地装的Mysql数据库版本为8.0.15，故原因为mysql驱动程序与mysql数据库版本不匹配。

解决方法

将mysql依赖换为高版本的8.0.12，同时注意将数据库配置文件进行更改，因为5.x和8.x版本的mysql驱动程序配置文件不一样

更改前的database.properties数据库配置文件，mysql-connector-java版本为5.1.38

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ums?useSSL=false&useUnicode=true&characterEncoding=UTF-8
jdbc.username=root
jdbc.password=123456

更改后的database.properties数据库配置文件，mysql-connector-java版本为8.0.12

jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ums?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC
jdbc.username=root
jdbc.password=123456

后记

2020刚开年就不太平哎，又是肺炎疫情，又是科比去世，希望这一切都能早点好起来