Sorting query results: can SQL ORDER BY sort by multiple columns (primary key, tie-breakers), or is it limited to only one column?

Introduction / Context:Sorting is fundamental in reporting and pagination. This question evaluates whether ORDER BY can handle multiple sort keys (e.g., last_name, first_name) or if it is limited to a single column.

Given Data / Assumptions:

• Standard SQL ORDER BY syntax is available.
• Columns may be named or referenced by ordinal or expression.
• We can specify ASC/DESC independently per key.

Concept / Approach:SQL ORDER BY supports a comma-separated list of expressions, each with its own direction. For instance, ... ORDER BY last_name ASC, first_name ASC; sorts primarily by last_name and uses first_name to break ties. This generalizes to any number of keys, including expressions (e.g., ORDER BY COALESCE(priority, 999), created_at DESC).

Step-by-Step Solution:

Verification / Alternative check:Run an example and compare: ORDER BY department, salary DESC clearly sorts first by department, then within each department by salary descending.

Why Other Options Are Wrong:

• “Correct” conflicts with the multi-key capability of ORDER BY.
• Limiting to numeric columns is false; text, dates, and expressions are allowed.
• ORDER BY does not depend on indexes to function, though indexes can affect performance.
• SORTING does not require GROUP BY.

Common Pitfalls:Relying on implicit sort order or assuming rows are returned in insertion order. Always specify ORDER BY explicitly for deterministic presentation.

Final Answer:Incorrect