Update ResultSet

Hi everyone,

I have a query including an inner join, which I execute to obtain a
ResultSet, but when I execute the following piece of code I get an error
message saying that it could not update the table because it could not
find the primary key for a table.
rs.first();
rs.updateString("gene", "TestGen");
rs.updateRow();

Here is my query:
SELECT gene_entropy.gene, gene_entropy.entropy, gene_entropy.iteration,
snp_entropy.snp_id
FROM clustering.gene_entropy INNER JOIN clustering.snp_entropy
USING(gene) limit 5;

And here is the stacktrace:
org.postgresql.util.PSQLException: Für die Tebelle
(clustering.gene_entropy konnte kein Primärschlüssel gefunden werden.
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.isUpdateable(AbstractJdbc2ResultSet.java:1547)
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.checkUpdateable(AbstractJdbc2ResultSet.java:2550)
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.updateValue(AbstractJdbc2ResultSet.java:2796)
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.updateString(AbstractJdbc2ResultSet.java:1309)
at
org.postgresql.jdbc2.AbstractJdbc2ResultSet.updateString(AbstractJdbc2ResultSet.java:1394)
at
myapp.ui.event.DBTableFrameListener.actionPerformed(DBTableFrameListener.java:406)
at
javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at
javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at
javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at
javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at
javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at
java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:272)
at java.awt.Component.processMouseEvent(Component.java:6038)
at
javax.swing.JComponent.processMouseEvent(JComponent.java:3260)
at java.awt.Component.processEvent(Component.java:5803)
at java.awt.Container.processEvent(Container.java:2058)
at java.awt.Component.dispatchEventImpl(Component.java:4410)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at
java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
at
java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
at
java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
at java.awt.Container.dispatchEventImpl(Container.java:2102)
at java.awt.Window.dispatchEventImpl(Window.java:2429)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
at
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
at
java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

I am more than happy and thankful for any advice!

Christian Rengstl M.A.
Klinik und Poliklinik für Innere Medizin II
Kardiologie - Forschung
Universitätsklinikum Regensburg
B3 1.388
Franz-Josef-Strauss-Allee 11
93053 Regensburg
Tel.: +49-941-944-7230