Pipeline help

Does a pipeline still update records when it errors out for unique fields. I am having hard time to figure. I am using Json to paste the records from report in parent table to create new records in the target child table. But it was creating duplicate records every time I ran. So I decided to make an ID field in target table as unique and mapped it to record id field of parent table. I ran it the first time it was smooth but second it gives me error  51. I just want the pipeline to update exisiting records in the report and creates new ones if they show up in the report. Any ideas regarding it?