android sqlite 数据库升级

场景：

　　数据库版本v1            有一个persion表

　　数据库版本v2             新增表student

　　数据库版本v3             persion表新增一个字段

package com.example.natedb;

import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;

public class SqlDb extends SQLiteOpenHelper {

    private final static int version = 3;
    public SqlDb(Context context){
        this(context,"lihao.db",null,version);
    }
    public SqlDb(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
        
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
    //    db.execSQL("create table person(_id integer primary key autoincrement,name text,age text)");
        //最新
        db.execSQL("create table person(_id integer primary key autoincrement,name text,age text,score txt)");
        db.execSQL("create table student(_id integer primary key autoincrement,name text,age text)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        int currentVersion = oldVersion;
        db.beginTransaction();
        try {
            if(currentVersion == 1) {
                db.execSQL("create table student(_id integer primary key autoincrement,name text,age text)");
                currentVersion = 2;
            }

            if(currentVersion == 2) {
                String tempTable = "person_temp";
                //修改原表为临时表
                db.execSQL("alter table person rename to "+tempTable);
                
                //创建新表
                db.execSQL("create table person(_id integer primary key autoincrement,name text,age text,score txt)");
                
                //复制数据
                db.execSQL("insert into person(name,age) select name,age from "+tempTable);
                
                //删除临时表
                db.execSQL("drop table "+tempTable);
            }
            db.setTransactionSuccessful();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally{
            db.endTransaction();
        }
        
        
    }

    
}