Android数据库升级，数据不丢失解决方案

protected void upgradeTables(SQLiteDatabase db, String tableName, String columns)  
{  
    try  
    {  
        db.beginTransaction();  
  
        // 1, Rename table.  
        String tempTableName = tableName + "_temp";  
        String sql = "ALTER TABLE " + tableName +" RENAME TO " + tempTableName;  
        execSQL(db, sql, null);  
  
        // 2, Create table.  
        onCreateTable(db);  
  
        // 3, Load data  
        sql =   "INSERT INTO " + tableName +  
                " (" + columns + ") " +  
                " SELECT " + columns + " FROM " + tempTableName;  
  
        execSQL(db, sql, null);  
  
        // 4, Drop the temporary table.  
        execSQL(db, "DROP TABLE IF EXISTS " + tempTableName, null);  
  
        db.setTransactionSuccessful();  
    }  
    catch (SQLException e)  
    {  
        e.printStackTrace();  
    }  
    catch (Exception e)  
    {  
        e.printStackTrace();  
    }  
    finally  
    {  
        db.endTransaction();  
    }  
}