how edit within condtion in gridview in asp.net,c#

hi

 

I am SQL Table with two columns.while binding in gridview,in need to edit and update the columns.condition is 1 st column values is always higher than second column,if its not following the rule in editing throw a massage as u cnt able enter more than the 1st column value.

 

ex:

 

table:

 

Id    sd        cd

1    1500    700

2    2000    1500

3    3000    2000

 

there sd is always > than cd.so while editing records to Id its should follow the conditions.

 

id      sd             cd

1     textbox1    textbox2

 

textbox1>textbox2 

 

 

how to able to edit in the gridview with this condition.?

help me.