How can we check the duplicate records in report service area.Is there any formulae by which we can give on any particular field so that we can have a check on duplicate records in report service area.
You can do a count(ID) by lastname,firstname and filter on that for all values greater than 1. This has 2 issues, if your dataset is large this will be slow and this will only work if the dups are exact in first and last name.
My suggestion is that you export to csv and then run a heuristic process on it to detect dups and then concat the 2 records and run a Data Loader batch to delete the dups and update the merged contact records. The reason I suggest this approach is because in your heuristic process you have all the flexibility to try different algorithms and compare results (and hopefully post them here so that others don't have to repeat the same thing).