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FC0-U71 Practice Question: A database administrator adds an index on the…
A database administrator adds an index on the 'Email' column of a 'Users' table. What is a likely consequence?
⚠ Common exam trap
Watch out — candidates often assume indexes universally speed up all database operations, ignoring the write-performance penalty that occurs because the index must be maintained on every INSERT, UPDATE, and DELETE.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Slower update operations on the table
Adding an index on the 'Email' column improves the speed of SELECT queries that filter or sort by that column, but it introduces overhead on write operations. Every time a row is inserted, updated, or deleted, the database must also update the index structure (e.g., a B-tree). This additional work makes UPDATE operations slower, which is why option C is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Reduced storage space
Why it's wrong here
An index consumes additional storage for its B-tree structure; it does not free space. Reduced storage suits removing redundant indexes or archiving obsolete rows, whereas adding one increases the database's footprint on disk and in memory.
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Improved query performance for all queries
Why it's wrong here
An index accelerates lookups and sorts on the indexed column, but inserts, updates and deletes must maintain it, and unrelated queries gain nothing. Claiming universal improvement ignores the write overhead and the column-specific nature of index benefit.
- ✓
Slower update operations on the table
Why this is correct
An index on Email accelerates lookups and joins on that column, but every INSERT, UPDATE or DELETE touching Email must also maintain the index structure. That extra write overhead makes update operations on the Users table slower.
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Faster inserts on the table
Why it's wrong here
Indexes add a separate B-tree structure that must be updated on every INSERT, so writes slow down rather than speed up. Faster inserts tempt because indexes genuinely accelerate SELECT lookups on the indexed column, making them the right choice when read performance on Email is the goal.
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