>  Exception Occurred
> 
> Duplicate key or integrity constraint violation message from server: "Duplicate entry '6758' for key 1"
> Exception stack 
> java.sql.SQLException: Duplicate key or integrity constraint violation message from server: "Duplicate entry '6758' for key 1"
> 	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:1997)
> 	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1167)
> 	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1278)
> 	at com.mysql.jdbc.Connection.execSQL(Connection.java:2247)
> 	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1772)
> 	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1619)
> 	at org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:101)
> 	at com.pku.judgeonline.servlet.SubmitServlet.doPost(Unknown Source)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
> 	at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
> 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
> 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
> 	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
> 	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
> 	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
> 	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
> 	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
> 	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
> 	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
> 	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
> 	at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
> 	at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
> 	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
> 	at java.lang.Thread.run(Thread.java:595)
>