If the requirement is to remove duplicate rows, use DISTINCT
If the requirement is to produce aggregates with grouping, use GROUP BY
Seeing Group By with no aggregates suggests that someone read the myth that group by is faster/better than DISTINCT and didn't do any tests.
Specify the query in the simplest, most obvious way, if after testing performance is inadequate then consider alternate query forms and test them. If they're faster great, if not, go back to the simple form.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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