When a unique index is being considered for a join or a search argument, the optimizer knows that the query will return one row per scan. The message includes the index type, the string “returns 1 row,” and a page estimate, which includes the number of index levels, plus one data page:
Unique clustered index found, returns 1 row, 2 pages
Unique nonclustered index found, returns 1 row, 3 pages
