【解决方案】Unknown system variable 'query_cache_size'

 java连接mysql 报错

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.<init>(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(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:270)

原因是mysql-connector-java的版本还是6.0.6，需要升级版本到8.0.11 ，这个报错就不存在了

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.11</version>
</dependency>