Not only is the explanation wrong, as several people have pointed out, it is also uses somewhat outdated terminology and is maybe confused about which version of SQL it refers to. The term "positive operator" was used in BoL for SQL 2000, but from SQL 2005 on that term is not used , the operator is called "unary plus" (presumably because MS relised that the term "positive operator" would be likely to confuse people when applied to a copy or no-op operator); but the question is clearly trying to trap people into mistaking =+ for += (why else would the first answer option be exactly what would be seen if the query had had += instead of =+), and += first appeared in SQL 2008, not in SQL 2000.