Android -- 面试 -- 数据库升级策略

@Override
    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        super.onDowngrade(db, oldVersion, newVersion);
    }

protected void upgradeTables(SQLiteDatabase db, String tableName, String columns)  
{  
    try  
    {  
        db.beginTransaction();  

        // 1, 将现有表重命名为临时表
        String tempTableName = tableName + "_temp";  
        String sql = "ALTER TABLE " + tableName +" RENAME TO " + tempTableName;  
        execSQL(db, sql, null);  

        // 2, 创建新表  
        //onCreateTable(db); 
        createNewTableX(db);

        // 3, 将临时表数据导入新表中
        sql =   "INSERT INTO " + tableName +  
                " (" + columns + ") " +  
                " SELECT " + columns + " FROM " + tempTableName;  

        execSQL(db, sql, null);  

        // 4, 删除临时表 
        execSQL(db, "DROP TABLE IF EXISTS " + tempTableName, null);  

        db.setTransactionSuccessful();  
    }  
    catch (SQLException e)  
    {  
        e.printStackTrace();  
    }  
    catch (Exception e)  
    {  
        e.printStackTrace();  
    }  
    finally  
    {  
        db.endTransaction();  
    }  
}