Which subquery returns a single value?

Answer: Option A

This question is about subqueries in MySQL. A subquery is a query nested inside another query.

Imagine you have a big box of toys, and you want to find a specific toy. A subquery is like a smaller box inside the big box that helps you narrow down your search.

The question asks which type of subquery returns only one value (like finding one specific toy).

Here's a breakdown of the options:

A: scalar - This is the correct answer! A scalar subquery returns one single value, like a number, a string, or a date.

B: column - A column subquery returns a set of values from a single column, like a list of names.

C: row - A row subquery returns a set of values that represent a single row from a table, like a list of information about one toy.

D: table - A table subquery returns an entire table, like the entire box of toys.

So the answer is Option A: scalar because a scalar subquery specifically returns only one single value.