Should not be greater than No of vacancies

Hi Team,



I am attempting to perform Summation of values of a text field in a detail, and I am attempting to compare the summation value and another field in another detail.



For Example.



Here I want to compare the sum on column assigned number field and the number of vacancies.if the sum on column assigned number exceeds the number of vacancies, then it should show a prompt.



Sum on column assigned number is the summation of the Assigned number.



Can u please tell me the procedure how to do this.



please find the attachment  below



Hoping for a positive reply.

Regards,



Manikanta.