DBS-C01 Workload-Specific Database Design Practice Question
Network Topology
A database administrator is troubleshooting a slow-performing query on an Amazon RDS for MySQL instance. The slow query log shows the above entry. Based on the exhibit, which index would most improve the query performance?
⚠ Common exam trap
The trap here is that candidates often pick a single-column index on `status` (Option B) thinking it will help the filter, but they overlook the need to also optimize the sort or range on `created_at`, which requires a composite index to avoid a filesort.
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
✓
Composite index on (`status`, `created_at`).
The query filters on `status` and then sorts or filters on `created_at`. A composite index on (`status`, `created_at`) allows MySQL to use the index for both the equality condition on `status` and the range or sort on `created_at`, avoiding a filesort and reducing row scans. This is the most efficient index for this query pattern.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Index on `created_at` only.
Why it's wrong here
Does not help filtering on status.
- ✗
Index on `status` only.
Why it's wrong here
Helps filtering but not sorting; still may need file sort.
- ✗
Full-text index on `status` and `created_at`.
Why it's wrong here
Full-text indexes are for text search, not this query.
- ✓
Composite index on (`status`, `created_at`).
Why this is correct
Covers both filter and sort, avoiding a full table scan.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.