SQLiteOpenHelpe创建更新数据库

public class MainActivity extends Activity implements OnClickListener {
private static final int INIT_DB_VERSION = 1;
private static final int UPGRADE_DB_VERSION = 2;
private Button bt1, bt2;
private MydbHelper dbh;
private SQLiteDatabase db;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bt1 = (Button) findViewById(R.id.button1);
bt2 = (Button) findViewById(R.id.button2);
bt1.setOnClickListener(this);
bt2.setOnClickListener(this);
}

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()) {
case R.id.button1:
dbh = new MydbHelper(getBaseContext(), INIT_DB_VERSION);
db = dbh.getWritableDatabase();
Toast.makeText(getBaseContext(), "创建数据库成功", Toast.LENGTH_LONG)
.show();
break;
case R.id.button2:
dbh = new MydbHelper(getBaseContext(), UPGRADE_DB_VERSION);
db = dbh.getWritableDatabase();
Toast.makeText(getBaseContext(), "更新数据库成功", Toast.LENGTH_LONG)
.show();
break;
}
}

@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
dbh.close();
}

}

public class MydbHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "mdb";
private static final String TAG = "MydbHelper";

public MydbHelper(Context context, int version) {
super(context, DB_NAME, null, version);
}

@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
Log.i(TAG, "Begin execute onCreate");
try {
db.beginTransaction();
String sql = "CREATE TABLE TBL_USER(_id INTEGER PRIMARY KEY,name TEXT NOT NULL)";
db.execSQL(sql);
db.setTransactionSuccessful();
} catch (Exception e) {
e.printStackTrace();
} finally {
db.endTransaction();
}
Log.i(TAG, "Excute onCreate completed");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
Log.i(TAG, "Begin excute onUpgrade");
try {
db.beginTransaction();
String upgradeSql = "ALTER TABLE TBL_USER ADD COLUMN created_dt timestamp NOT NULL DEFAULTE '2010-10-01' COLLATE NOCASE;";
db.execSQL(upgradeSql);
db.setTransactionSuccessful();
} catch (Exception e) {
e.printStackTrace();
} finally {
db.endTransaction();
}
Log.i(TAG, "Excute onUpgrade completed");
}
}