我在MySQL中有一个表，名称为“ clienttable”，它有11列，第9列是“ yahooId”，第11列是“ password”。我有两个例外：1：行rst = stmt.executeQuery("SELECT yahooId AND password FROM clienttable");和2的SQL语法：while (rst.next())行的NullPoniterException，请帮助我，谢谢。
这也是我在数据库类中写的：
public static boolean Test(String userName, String password) {
boolean bool = false;
Statement stmt = null;
try {
stmt = conn.createStatement();
} catch (SQLException ex) {
Logger.getLogger(Manager.class.getName()).log(Level.SEVERE, null, ex);
}
ResultSet rst = null;
try {
rst = stmt.executeQuery("SELECT yahooId AND password FROM clienttable");
} catch (SQLException ex) {
Logger.getLogger(Manager.class.getName()).log(Level.SEVERE, null, ex);
}
try {
while (rst.next()) {
if (rst.getString(9).equals(userName) && rst.getString(11).equals(password)) {
bool = true;
} else {
bool = false;
}
}
} catch (SQLException ex) {
Logger.getLogger(Manager.class.getName()).log(Level.SEVERE, null, ex);
}
return bool;
}
例外：
init:
deps-jar:
compile-single:
run-single:
Jan 10, 2010 6:45:52 PM ClientDataBase.Manager Test
SEVERE: null
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM clienttable' at line 1
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.Util.getInstance(Util.java:381)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1030)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1383)
at ClientDataBase.Manager.Test(Manager.java:94)
at ClientGUI.MainFrame.submit(MainFrame.java:374)
at ClientGUI.MainFrame.jButton1ActionPerformed(MainFrame.java:257)
at ClientGUI.MainFrame.access$600(MainFrame.java:33)
at ClientGUI.MainFrame$7.actionPerformed(MainFrame.java:143)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$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.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
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)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ClientDataBase.Manager.Test(Manager.java:99)
at ClientGUI.MainFrame.submit(MainFrame.java:374)
at ClientGUI.MainFrame.jButton1ActionPerformed(MainFrame.java:257)
at ClientGUI.MainFrame.access$600(MainFrame.java:33)
at ClientGUI.MainFrame$7.actionPerformed(MainFrame.java:143)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$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.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
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)
最佳答案
您的选择应为：
选择yahooId，密码来自clienttable
您有一个AND而不是逗号。由于查询无效，因此不会返回ResultSet，并且您会得到null指针。
编辑：
您的查询将返回一个结果集，而不是您想要的结果集。 yahooId AND password将返回一列-这些列上逻辑AND的结果。然后，当您访问rs.getString（“ yahooId”）时，将返回null，并且您在那里便有一个.equals（）。根本问题是您需要逗号，但是我为null的原因是错误的。
编辑2：
我尝试查询，并且它在我的mysql上有效。也许这是一个版本的东西。无论如何，对于他的问题，我在编辑之前是正确的。