Final answer:
A scalar subquery must return a single value, and an error occurs if it produces more than one element. It often indicates that the query logic needs to be revised to properly use WHERE clauses or aggregation functions.
Step-by-step explanation:
The correct answer is option that a scalar subquery that produces more than one element results in an error condition in SQL. A scalar subquery is used when a single value is expected as a result; it should return exactly one row with one column. If the subquery accidentally fetches more than one row or element, this violates the expectation of a single value and hence causes an error because the calling context cannot handle multiple values.
For instance, if you have a SQL statement where you need the maximum price of a product, a scalar subquery can be used:
SELECT ProductName, (SELECT MAX(Price) FROM Products WHERE CategoryID = p.CategoryID) as MaxPrice FROM Products p;
This works as long as the subquery returns one price. However, if it mistakenly returns a list of prices, you will encounter an error stating that the subquery returned more than one value. This is usually a sign that your query logic needs to be revised, possibly including additional WHERE clause conditions or using aggregation functions like MAX() or MIN() correctly to ensure a single value is returned.