O'Reilly logo
  • Dustin Waybright thinks this is interesting:

Note that if what’s supposed to be a scalar subquery returns in practice more than one value, the code fails at run time. If the scalar subquery returns an empty set, it is converted to a NULL.

From

Cover of Training Kit (Exam 70-461): Querying Microsoft® SQL Server® 2012

Note

Scalar = single-value