How to SELECT data from in-memory Derby database table?

Question

I have created an in-memory database table using JavaDB/Derby. I can INSERT data into the table. But it doesn't work when I try to SELECT data from the table.

I create the table with:

DECLARE GLOBAL TEMPORARY TABLE SESSION.memtable (id int, name varchar(10))
NOT LOGGED

insert data with:

INSERT INTO SESSION.memtable (id, name) VALUES (?,?)

and it returns 1 for rows affected. I select data with:

SELECT name FROM SESSION.memtable WHERE id = ?

but it return an empty ResultSet (rs.next() is false).

What am I doing wrong when using SELECT?

I use the derby.jar that is included in JDK7.

Here is my code:

public class DBTest {
    public static void main(String[] args) {
        final int userId = 4;
        final String sql = "DECLARE GLOBAL TEMPORARY TABLE SESSION.memtable "+
                            "(id int, name varchar(10)) NOT LOGGED";
        final String inSQL = "INSERT INTO SESSION.memtable (id, name) "+
                             "VALUES (?,?)";
        final String selSQL = "SELECT name FROM SESSION.memtable WHERE id = ?"
        final String connURL = "jdbc:derby:memory:memdatabase;create=true";
        try(Connection conn = DriverManager.getConnection(connURL);) {
            try (PreparedStatement ps = conn.prepareStatement(sql);) {
                ps.execute();
            }
            try (PreparedStatement ps = conn.prepareStatement(inSQL);) {
                ps.setInt(1, userId);
                ps.setString(2, "Jonas");
                int rows = ps.executeUpdate();
                System.out.println(rows + " rows inserted.");
            }
            try (PreparedStatement ps = conn.prepareStatement(selSQL);) {
                ps.setInt(1, userId);
                try (ResultSet rs = ps.executeQuery();) {
                    String name;
                    if(rs.next()) {
                        name = rs.getString("name");
                    } else {
                        name = null;
                    }
                    System.out.println("Name: " + name);
                }
            }
        } catch (SQLException e) {e.printStackTrace();}}}

UPDATE

If I change the SELECT-query to:

SELECT t1.name AS name FROM SESSION.memtable t1 WHERE id = ?

I get this error message:

java.sql.SQLException: Operation 'DROP TABLE' cannot be performed on object 'MEMTABLE(ID, NAME)' because there is an open ResultSet dependent on that object.
    at org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedConnection.commitIfAutoCommit(Unknown Source)
    at org.apache.derby.impl.jdbc.ConnectionChild.commitIfAutoCommit(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedStatement.resultSetClosing(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedResultSet.movePosition(Unknown Source)
    at org.apache.derby.impl.jdbc.EmbedResultSet.next(Unknown Source)
    at DBTest.main(DBTest.java:29)
Caused by: java.sql.SQLException: Operation 'DROP TABLE' cannot be performed on object 'MEMTABLE(ID, NAME)' because there is an open ResultSet dependent on that object.
    at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
    at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown Source)
    ... 11 more
Caused by: ERROR X0X95: Operation 'DROP TABLE' cannot be performed on object 'MEMTABLE(ID, NAME)' because there is an open ResultSet dependent on that object.
    at org.apache.derby.iapi.error.StandardException.newException(Unknown Source)
    at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.verifyNoOpenResultSets(Unknown Source)
    at org.apache.derby.impl.sql.GenericPreparedStatement.prepareToInvalidate(Unknown Source)
    at org.apache.derby.impl.sql.depend.BasicDependencyManager.coreInvalidateFor(Unknown Source)
    at org.apache.derby.impl.sql.depend.BasicDependencyManager.invalidateFor(Unknown Source)
    at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.tempTablesAndCommit(Unknown Source)
    at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.doCommit(Unknown Source)
    at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.userCommit(Unknown Source)
    at org.apache.derby.impl.jdbc.TransactionResourceImpl.commit(Unknown Source)
    ... 6 more

But Name: is not printed, so it still doesn't work.

Answer 1

The question was discussed on the derby-user mailing list, where the additional requirement to include on commit preserve rows was noted.

With autocommit on, a temporary table by default is cleared at commit, so the extra clause ensures that the rows are kept available beyond transaction commit.