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CS422
NullPointerException

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lishenyu Posts: 103	Posted 23:03 Nov 09, 2015 \| Hi Dr.Sun, I have deleted the previous project and re-import SimpleDB project , but when I run it and no matter what query I typed , it still gave me NullPointerException : SQL Exception: java.lang.NullPointerException java.sql.SQLException: java.lang.NullPointerException at simpledb.remote.SimpleStatement.executeQuery(SimpleStatement.java:24) at simpledb.client.SQLInterpreter.doQuery(SQLInterpreter.java:48) at simpledb.client.SQLInterpreter.main(SQLInterpreter.java:26) Caused by: java.lang.NullPointerException at simpledb.record.Schema.type(Schema.java:105) at simpledb.record.Schema.add(Schema.java:65) at simpledb.query.ProjectPlan.<init>(ProjectPlan.java:23) at simpledb.planner.BasicQueryPlanner.createPlan(BasicQueryPlanner.java:40) at simpledb.planner.Planner.createQueryPlan(Planner.java:29) at simpledb.remote.RemoteStatementImpl.executeQuery(RemoteStatementImpl.java:31) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:323) at sun.rmi.transport.Transport$1.run(Transport.java:200) at sun.rmi.transport.Transport$1.run(Transport.java:197) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Transport.java:196) at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$254(TCPTransport.java:683) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$1/739018661.run(Unknown Source) could you help me solve this ?Thanks!
cysun Posts: 2935	Posted 08:26 Nov 10, 2015 \| Did you create any table before trying to "select"?
lishenyu Posts: 103	Posted 09:52 Nov 10, 2015 \| I just start the server first then run the client , and in console it prompts to ask for SQL> ,then I type easy query like "select id from students; " then this nullpointerexception occurs
cysun Posts: 2935	Posted 09:55 Nov 10, 2015 \| lishenyu wrote: I just start the server first then run the client , and in console it prompts to ask for SQL> ,then I type easy query like "select id from students; " then this nullpointerexception occurs Sounds like you didn't create a students table or the students table didn't have a column id.
lishenyu Posts: 103	Posted 10:11 Nov 10, 2015 \| isn't it that when we run the client ,it automaticly creates a student DB? I need to create student DB? but yesterday I didn't create any tables , at first it can run the basic query but then for some reason ,it results in this exception.
lishenyu Posts: 103	Posted 10:14 Nov 10, 2015 \| because I have seen code of CreateStudentDB in same folder in Client folder , so I think ,when we specify no arguments ,it will automatically create a StudentDB.
cysun Posts: 2935	Posted 10:27 Nov 10, 2015 \| When you run the server, if no database exists, it will create an empty StudentDB. There are several client programs. Read the code to see what each client does.