mysql数据库中，查询一个表的下一条数据减上一条数据的值的写法

mysql数据库中，查询一个表的下一条数据减上一条数据的值的写法：

select 
    a.nodeId,
    a.cpuCharge-b.cpuCharge cpuCharge, 
    a.chargeTime from
(select @arownum:=@arownum+1 rownum,nodeId,cpuCharge,chargeTime from rn_ext_vir_instance_charge_history,(select @arownum:=0) t where nodeId = 318263374 order by chargeTime) a,
(select @brownum:=@brownum+1 rownum,nodeId,cpuCharge,chargeTime from rn_ext_vir_instance_charge_history,(select @brownum:=1) t where nodeId = 318263374 order by chargeTime) b
where a.rownum = b.rownum;