The syntax for comparison predicates is as follows:

In a comparison predicate, expression2 can be a subquery. If expression2 is a subquery and does not return any rows, the comparison predicate evaluates to false. For information about subqueries, see Subqueries. For details about comparison operators, see Comparison Operators.

If an operand is a row valued expression, then the other operand must also be one unless it is a subquery. In either case, the number of elements in the row values or subquery results must match.