### Cause: java.sql.SQLException: Unknown system variable 'query_cache_size' 解决方案

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

Sat May 18 11:02:46 CST 2019 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: java.sql.SQLException: Unknown system variable 'query_cache_size'
### The error may exist in com/gxkj/lcf/mapper/GoodsTypeMapper.xml
### The error may involve com.gxkj.lcf.mapper.GoodsTypeMapper.findAll
### The error occurred while executing a query
### 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.selectList(DefaultSqlSession.java:150)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
	at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:137)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:75)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
	at com.sun.proxy.$Proxy2.findAll(Unknown Source)
	at com.gxkj.lcf.run.MyBatisUsage.main(MyBatisUsage.java:26)
Caused by: java.sql.SQLException: Unknown system variable 'query_cache_size'
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:545)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:513)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:115)
	at com.mysql.cj.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:1983)
	at com.mysql.cj.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:1936)
	at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1422)
	at com.mysql.cj.jdbc.ConnectionImpl.loadServerVariables(ConnectionImpl.java:2831)
	at com.mysql.cj.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:2381)
	at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:1739)
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:1596)
	at com.mysql.cj.jdbc.ConnectionImpl.(ConnectionImpl.java:633)
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:347)
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:219)
	at java.sql.DriverManager.getConnection(Unknown Source)
	at java.sql.DriverManager.getConnection(Unknown Source)
	at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:201)
	at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.doGetConnection(UnpooledDataSource.java:196)
	at org.apache.ibatis.datasource.unpooled.UnpooledDataSource.getConnection(UnpooledDataSource.java:93)
	at org.apache.ibatis.datasource.pooled.PooledDataSource.popConnection(PooledDataSource.java:404)
	at org.apache.ibatis.datasource.pooled.PooledDataSource.getConnection(PooledDataSource.java:90)
	at org.apache.ibatis.transaction.jdbc.JdbcTransaction.openConnection(JdbcTransaction.java:139)
	at org.apache.ibatis.transaction.jdbc.JdbcTransaction.getConnection(JdbcTransaction.java:61)
	at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
	at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:84)
	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
	... 6 more

这是一个数据库驱动版本问题
解决方法（在pom.xml中改数据库驱动版本）：

			mysql
			mysql-connector-java
			6.0.6
		

改为：

			mysql
			mysql-connector-java
			8.0.11
		

保存再运行就可以了