Which statement best explains how sorting data by multiple columns works?

Which statement best explains how sorting data by multiple columns works?

• A. The secondary key defines the next level of ordering within ties of the primary key
• B. The primary key is applied again
• C. The data is randomly shuffled
• D. The last column is used

Answer: (A)

When sorting data by more than one column, you establish a hierarchy of keys. The first column you sort by sets the overall order, and if two rows share the same value in that primary column, the next column in your sort becomes the tiebreaker. If those also match, a third column can serve as another level of ordering, and so on. This is exactly what the statement means: the secondary key defines the next level of ordering within ties of the primary key. For example, sort a list by city first; within the same city, sort by last name to determine the order. If there were a third column, it would break ties further. The other ideas—reapplying the primary key, shuffling the data, or using only the last column—don’t describe how multi-column sorting creates a stable, hierarchical order when the primary values are equal.

When sorting data by more than one column, you establish a hierarchy of keys. The first column you sort by sets the overall order, and if two rows share the same value in that primary column, the next column in your sort becomes the tiebreaker. If those also match, a third column can serve as another level of ordering, and so on. This is exactly what the statement means: the secondary key defines the next level of ordering within ties of the primary key. For example, sort a list by city first; within the same city, sort by last name to determine the order. If there were a third column, it would break ties further. The other ideas—reapplying the primary key, shuffling the data, or using only the last column—don’t describe how multi-column sorting creates a stable, hierarchical order when the primary values are equal.