mysql數據庫中，查詢一個表的下一條數據減上一條數據的值的寫法

mysql數據庫中，查詢一個表的下一條數據減上一條數據的值的寫法：

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;