尝试通过从TextField读取值来创建新数据库。在创建数据库之前，我决定检查它是否存在。我的代码如下。
public void createAccount() throws ClassNotFoundException, SQLException {
try {
dbName = t12.getText();
Class.forName("com.mysql.jdbc.Driver");
connect = DriverManager
.getConnection("jdbc:mysql://localhost:3306/project?"
+ "user=root&password=virus");
statement = connect.createStatement();
preparedStatement = connect
.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = "+dbName+"");
rs=preparedStatement.executeQuery();
rs.next();
int chk = rs.getInt(1);
if(chk!=1)
{
int resultset = statement.executeUpdate("create database " + dbName );
connect = DriverManager
.getConnection("jdbc:mysql://localhost:3306/"+ dbName +"?"
+ "user=root&password=virus");
statement = connect.createStatement();
preparedStatement = connect
.prepareStatement("create table " + dbName + " (fullname varchar(30),"
+ "username varchar(20) primary key, password varchar(20),"
+ "department varchar(30), semester int(2));");
preparedStatement.executeUpdate();
preparedStatement = connect
.prepareStatement("insert into " + dbName + " values(?,?,?,?,?);");
preparedStatement.setString(1, t11.getText());
preparedStatement.setString(2, t12.getText());
preparedStatement.setString(3, p11.getText());
preparedStatement.setString(4, t13.getText());
preparedStatement.setString(5, (String)comboBox.getValue());
preparedStatement.executeUpdate();
}
else
{
actiontarget = new Text();
actiontarget.setFill(Color.FIREBRICK);
actiontarget.setText("Try another User Name...!");
actiontarget.setFont(Font.font(null, 15));
setEffect(new BoxBlur(5, 10, 10));
Stage usrpagestage = new Stage();
usrpagestage.setMaxHeight(60);
usrpagestage.setMaxWidth(200);
usrpagestage.initStyle(StageStyle.UTILITY);
usrpagestage.setScene(new Scene(new Warning()));
usrpagestage.show();
usrpagestage.setOnCloseRequest(new EventHandler<WindowEvent>() {
@Override
public void handle(WindowEvent t) {
setEffect(new BoxBlur(0, 0, 0));
}
});
}
} catch (ClassNotFoundException | SQLException e) {
throw e;
} finally {
close2();
}
}
我运行了这段代码。我填写表格中的所有字段并按下按钮。然后我得到了这个例外 -
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'poi' in 'where clause'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1053)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4120)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4052)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2503)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2664)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2794)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2322)
at frontpage.FrontPage.createAccount(FrontPage.java:335)
at frontpage.FrontPage$8.handle(FrontPage.java:308)
at frontpage.FrontPage$8.handle(FrontPage.java:304)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Node.fireEvent(Node.java:6867)
at javafx.scene.control.Button.fire(Button.java:179)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3311)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3151)
at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3106)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1563)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2248)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:250)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:173)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:292)
at com.sun.glass.ui.View.handleMouseEvent(View.java:530)
at com.sun.glass.ui.View.notifyMouse(View.java:924)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:17)
at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:67)
at java.lang.Thread.run(Thread.java:744)
为什么会生成此异常？我该如何解决？
答案 0 :(得分：2)
preparedStatement = connect
.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = "+dbName+"");
到
preparedStatement = connect
.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
" WHERE table_schema = '"+dbName+"'");
你需要用字母用单引号括起where值，否则它会抛出错误。
这是一个例子
mysql> SELECT COUNT(*) FROM information_schema.tables where table_schema = users ;
ERROR 1054 (42S22): Unknown column 'users' in 'where clause'
mysql> SELECT COUNT(*) FROM information_schema.tables where table_schema = 'users' ;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
答案 1 :(得分：0)
您没有以正确的方式使用PreparedStatement。
使用占位符?将值输入到查询中。通过使用set...方法，您可以将值设置为查询中的各种参数。
这对于处理转义字符和sql注入是安全的。
table_schema = poi的情况不会发生。但内部注意为table_name = 'poi'。
更改：
preparedStatement =
connect.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = "+dbName+"");
rs=preparedStatement.executeQuery();
到：
String sqlQuery = "SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = ?";
preparedStatement =
connect.prepareStatement( sqlQuery );
preparedStatement.setString( 1, dbName );
rs=preparedStatement.executeQuery();
答案 2 :(得分：0)
您的查询错误。
preparedStatement = connect
.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = "+dbName+"");
那是错的。始终用单引号传递参数名称，如下所示：
preparedStatement = connect
.prepareStatement("SELECT COUNT(*) FROM information_schema.tables \n" +
"WHERE table_schema = '"+dbName+"'");