What is a consequence of adding indexes on a database table?

• A. They speed up lookups and range queries but slow inserts/updates and consume storage.
• B. They never affect performance.
• C. They reduce storage requirements.
• D. They speed up writes.

Answer: (A)

Indexes provide a fast path to locate rows by the indexed column(s), so lookups and range queries can find results without scanning the entire table. This is why they noticeably speed reads on large datasets.

But keeping an index up to date requires work every time data changes. Inserts, updates, or deletes must also modify the index structure, which adds overhead and slows those write operations. In addition, the index itself takes extra storage space beyond the table data, since the index stores its own data structures and pointers.

So, the practical effect is faster reads for targeted queries, paired with slower writes and increased storage usage. Other choices are incorrect because they claim no performance impact, reduced storage, or faster writes, which don’t align with how indexes operate.