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FC0-U71 Practice Question: That a SELECT query on a large table with…
A user reports that a SELECT query on a large table with millions of records is very slow. The table has no indexes. Which index type would most likely improve the performance of equality searches (e.g., WHERE id = 100)?
⚠ Common exam trap
A common mix-up: candidates confuse 'nonclustered index' as the default or best choice for all searches, but for equality searches on a large table, a clustered index eliminates the extra lookup step and is the most performant option.
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
✓
Clustered index on the column
A clustered index on the column used in equality searches (e.g., WHERE id = 100) is the most effective because it physically reorders the table data in the same order as the index key. This allows the database engine to perform a single seek operation directly to the exact row, rather than scanning millions of records. For a large table with no indexes, a clustered index provides the fastest possible access for equality lookups on the indexed column.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Full-text index on the column
Why it's wrong here
Full-text index is designed for text search (like CONTAINS), not for simple equality on numeric or short strings.
- ✗
Nonclustered index on the column
Why it's wrong here
A nonclustered index stores a separate structure; it can help but clustered is often faster for equality on large tables.
- ✓
Clustered index on the column
Why this is correct
A clustered index sorts and stores the data rows in order, making equality lookups very fast via binary search.
- ✗
Unique index on the column
Why it's wrong here
A unique index is typically nonclustered by default unless specified; it does not inherently improve performance more than a nonclustered index.
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