Index Question Explained
This worked SQL Fundamentals practice question tests Performance. Try the answer first, then review why A is the best choice.
Short answer
The correct answer is A. Speed up lookups and joins on indexed columns.
Indexes help the database find matching rows faster, especially for selective filters and join keys. They also add write overhead. The key is to match the exact action in the prompt to the tool, command, or concept that performs that action directly. Here, A. Speed up lookups and joins on indexed columns is the only option that satisfies the scenario without adding unrelated behavior.
The Question
What is a common purpose of an index?
Why A is correct
Indexes help the database find matching rows faster, especially for selective filters and join keys. They also add write overhead. The key is to match the exact action in the prompt to the tool, command, or concept that performs that action directly. Here, A. Speed up lookups and joins on indexed columns is the only option that satisfies the scenario without adding unrelated behavior.
Why the other options are wrong
Option B does not match the requirement in the prompt. The correct answer is A because Indexes help the database find matching rows faster, especially for selective filters and join keys. They also add write overhead.
Option C does not match the requirement in the prompt. The correct answer is A because Indexes help the database find matching rows faster, especially for selective filters and join keys. They also add write overhead.
Option D does not match the requirement in the prompt. The correct answer is A because Indexes help the database find matching rows faster, especially for selective filters and join keys. They also add write overhead.
Key idea: Performance
Performance questions test whether you can connect a common workflow problem to the right practical command, service, or concept. Instead of memorizing isolated definitions, look for the job being done in the prompt: staging a file, querying rows, running code, persisting container data, checking a service, or choosing the right cloud building block. The best answer usually names the simplest tool that performs that job directly. For SQL Fundamentals, the safest study pattern is to read the scenario, underline the action verb, and eliminate answers that solve a different problem. If an option sounds related but changes the scope, adds risk, or describes a different layer of the stack, it is probably a distractor. After choosing an answer, explain why the other three fail; that habit builds the practical judgment these quizzes are meant to measure.
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