Multiple grid lines edit

Scenario is I have 2 columns in my app where multiple lines will be there for same address number out of which any one line will be having "Y " as column 2. Now user is allowed to edit these lines and I should throw some error message when ever a single address number set of lines has more than one "Y" in second column i.e user should be limited to enter a new line or even edit existing lines with one "Y " for every single address numbr set.

If somebody has seen such problem please throw some light.

thanks in advance.

You want to make column 2 unique for a value of 'Y'?

When they exit the column just loop through the grid and check if it exists more than once (1 being the value just exited)

I am able to check and throw error message when ever user changes value in some column for same aN8 set of lines. But here the problem is some times user may interchange Y,N values where I am unable to clear the error messages set to prior lines.