我需要提出一个计算值......
FOR EX：
FLD1 FLD2 FLD3
a 100 10
a 20
a 30
我需要以这种方式出局
FLD1 FLD2 FLD3 diff
a 100 10 90 (fld2-fld3)
a 20 70(diff of prev row -fld3)
a 30 40 (diff of prev row -fld3)
我无法对diff进行延迟，因为它是一个计算列
先谢谢