Unknownsystemvariablequery_cache_size错误原因以及解决办法
Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apachemons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory ### 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/l]
### The error may involve cn.ydyfc.chuan_zang_help.dao.AdminMapper.selectAllAdmins
### The error occurred while executing a query
手机unknown是什么意思### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apachemons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Unknown system var java.sql.SQLException: Unknown system variable 'query_cache_size'
sql.ateSQLException(SQLError.java:964)
sql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
sql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
sql.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。

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