check for column value and update value in that row in sql

Question

geeks,

plz help me with sql query

i have a table like this

p_name	qty	batchno	vendor	Odr flag
disprin	20	b5	A	ordered
crocin	5	d3	B	null
disprin	12	b6	B	ordered
(new insert)	2	g3	w	null

you see here disprin is indicating ordered from Odr flag

while crocin has null value in odr flag as not been ordered yet .

now i want when i insert another entry (for example disprin) then query checks if its Odr col has value 'Ordered' then update it as null in all the rows having P_name 'disprin' . 

so on inserting disprin it should be like this

p_name	qty	batchno	vendor	Odr flag
disprin	20	b5	A	null
crocin	5	d3	B	null
disprin	12	b6	B	null
disprin	2	g3	w	null

 help me guys. any help will be appreciated .