We have to dates Date Identified and Due Date in the OOB Issue Request Type. but there is no rule around that. What we want is to have the Due Date should not be selected before Date Identified. I would like to do this by using SQL rule rather than going with UI rule.
but when the user in entering a new Issue they want both these fields and the problem is that when they enter Date Identified they do not want to enter a due date of before the one enter in Date Identified ... it is like when you create a project and enter start date and end date ........you cannot enter the end date before the start date.
Have a look at the validation that is used for the planned finish period in the default projekt details requests. It uses a request token for filtering the periods. If I got you right, you want to have to date fields (not periods), so what you need for this is a custom date validation for the second field, that includes a similar filter dependent on the first date field. Unfortunately validations of type "date" are not very customizable. So best way would be UI rules or have the first wf-step validate the dates as Mahen suggested. If it fails -> back to a rework step for the creator.