Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Unknown system variable 'query_cache_size')
### The error may exist in file [/Volumes/mac/Eclipse Project/Tomcat_version/apache-tomcat-9.0.21/webapps/chuan_zang_help/WEB-INF/classes/cn/ydyfc/chuan_zang_help/mapper/AdminMapper.xml]
### The error may involve cn.ydyfc.chuan_zang_help.dao.AdminMapper.selectAllAdmins
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Unknown system variable 'query_cache_size')] with root cause
java.sql.SQLException: Unknown system variable 'query_cache_size'
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:964)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2527)

错误提示：Cannot create PoolableConnectionFactory (Unknown system variable 'query_cache_size')

原因：由于mysql驱动包的版本过低导致这个问题的发生意思是query cache在MySQL5.7.20就已经过时了，而在MySQL8.0之后就已经被移除了。

我改成8以上才可以了。