5 exercises — choose the best-structured answer to common DBA interview questions. Focus on precise database terminology, trade-off reasoning, and production-aware thinking.
Structure for DBA interview answers
Define precisely: use the exact technical term, not just a synonym
Mechanism: explain how it works at the storage or transaction level
Trade-off: name what you gain and what you sacrifice
Production context: show awareness of real-world constraints (locks, downtime, replication)
0 / 10 completed
1 / 10
The interviewer asks: "Can you explain ACID properties?" Which answer demonstrates the deepest understanding?
Option A is the strongest: it defines each property with a precise, single-sentence definition that captures the essential mechanism. Key signals of depth: "brings the database from one valid state to another, respecting all constraints" (not just "keeps data valid"), and "concurrent transactions execute as if they were sequential" (explains the isolation model). Option C mentions write-ahead logging — an excellent implementation detail — but defines isolation as "prevents dirty reads" which is incomplete (isolation covers dirty reads, non-repeatable reads, and phantom reads at various levels). Option D is accurate but uses informal phrasing ("writes survive a restart"). Option B is too brief to show depth. For ACID: give the full noun phrase for each property and the exact mechanism, not just a synonym.
2 / 10
The interviewer asks: "What is the difference between a clustered and a non-clustered index?" Choose the most technically precise answer.
Option A is the best: it explains why only one clustered index is possible (data rows are physically ordered and stored according to the clustered key), explains what a non-clustered index contains (indexed columns plus a pointer back to the actual row), and gives practical guidance on when to use each. Option C is also strong — mentioning SQL Server's default PK behaviour and the difference between a clustered key pointer vs file/row pointer shows implementation awareness. Option D's "clustered index = the table" is a memorable shorthand but too informal. Option B is accurate but lacks the "why" behind the one-clustered-index limit. Key tip: explain the "why only one clustered" constraint — it signals you understand the physical storage model.
3 / 10
The interviewer asks: "How do you approach query optimisation when a slow query is reported?" Which answer shows the best professional process?
Option A is the strongest process description: it starts with the right tool (EXPLAIN/EXPLAIN ANALYZE), lists multiple specific signals to look for in the plan (full scans, row estimate errors, nested loops, sort operations), covers indexes on all relevant clause types (WHERE, JOIN, ORDER BY), mentions statistics staleness, gives a specific rewrite example (correlated subquery → CTE/join), and adds the implicit type conversion trap — a detail that only experienced DBAs usually mention. Option C is good and mentions partitioning — showing awareness of large-scale solutions. Option D's approach of asking the developer for context first is actually very professional and often overlooked by purely technical candidates. Option B is too basic for a DBA interview. Structure: explain → identify bottlenecks → fix indexes → refactor query → check statistics.
4 / 10
The interviewer asks: "What is database normalisation and when would you denormalise?" Choose the most complete and balanced answer.
Option A is the strongest: it defines normalisation precisely (reduce data redundancy and improve data integrity), names the mechanism (normal forms, 1NF–BCNF), explains what the forms eliminate (insertion, update, or deletion anomalies), and gives the exact condition for denormalisation (read performance outweighs write integrity concerns) with a specific real-world context (analytical/reporting) and a concrete trade-off statement. Option C is also excellent — distinguishing OLTP (3NF) from data warehouse (star/snowflake) shows architectural maturity and real-world experience. Option D is accurate and mentions the anomalies, which is a strong signal. Option B is too brief. Tip: the best DBA answer always names the trade-off — normalisation favours write integrity; denormalisation favours read performance.
5 / 10
The interviewer asks: "How do you handle database migration in a high-availability production environment?" Choose the most professionally structured answer.
Option A is the best: it names the key principle (backward-compatible migrations — the old app version must work with new schema), explains the phased approach for destructive changes (add → deploy → drop), names specific industry tools (pt-online-schema-change, gh-ost), mentions the rollback plan requirement, and notes low-traffic windows. Option C names the "expand-contract pattern" — expert-level vocabulary that shows architectural awareness. Option B is sensible but lacks the backward-compatibility principle and doesn't mention specific tools. Option D's approach (backup → run → rollback from backup) describes a naive strategy with high risk — restoring from backup in a HA environment causes significant downtime. Key insight: the critical principle is backward compatibility between schema and application code during rolling deploys.
6 / 10
Sarah (Senior DBA) sends you this Slack message: 'Hey, the SELECT * FROM users WHERE last_login > '2023-10-26' query is timing out. It's impacting user onboarding. Any ideas?' Which response best demonstrates a proactive approach to troubleshooting and aligns with DBA responsibilities?
The correct answer focuses on *diagnosis* before escalation. Simply restarting the server is a reactive band-aid; running `EXPLAIN` is a standard DBA technique for identifying inefficient queries. Scaling up without understanding the root cause is premature and potentially wasteful. Monitoring KPIs provides valuable data to understand and prevent future occurrences.
7 / 10
You're reviewing a Pull Request with this commit message: 'Added index on user_id in the orders table.' The developer explains this was done to improve query performance for retrieving order details. Which of the following statements best reflects your feedback as a DBA?
While adding an index *can* improve read performance, it's crucial for DBAs to recognize that indexes also slow down write operations (inserts, updates, deletes). A good DBA considers both read and write performance implications. Simply stating 'it always improves query speed' is an oversimplification.
8 / 10
Mark (a Developer) reports: 'The API endpoint for retrieving customer data is slow.' You investigate and find a complex `SELECT` statement with multiple joins. Which approach would you *most* effectively communicate to Mark regarding the optimization strategy?
The correct response emphasizes *collaboration* and providing Mark with tools (the `EXPLAIN` statement) to understand the problem. Simply giving him a script bypasses his learning opportunity and doesn't address the underlying issue of inefficient SQL. Suggesting a new server is an expensive solution without diagnosing the root cause.
9 / 10
During a standup meeting, you're asked about your progress on database schema changes. You respond: 'I've implemented a new normalization strategy for the product catalog table to reduce redundancy and improve data integrity.' Which of the following is the *most* appropriate follow-up question from the team lead?
The most effective follow-up question seeks *understanding* and justification for the change. Simply asking for a diagram is a technical detail; requesting an explanation of the benefits demonstrates that you've considered the broader implications of your work. A rollback plan is important but shouldn't be the initial focus.
10 / 10
You are tasked with migrating a large database to a new cluster in a high-availability production environment. Which statement best describes your approach from a DBA perspective?
A high-availability environment demands careful planning to avoid service disruption. Phased migration using replication is the standard approach for minimizing downtime. Monitoring metrics and having a rollback plan are critical components of any successful migration strategy.
What does "Database Administrator Interview Questions — Best-Answer Practice" cover?
Practice answering common DBA interview questions in professional English. 5 exercises on ACID, indexes, query optimisation, normalisation, and production migrations.
How many questions are in this interview set?
This set has 10 exercises, each with a full explanation.
Is this exercise free to use?
Yes. Every exercise on CoderSlingo, including this one, is free to use with no account, sign-up, or paywall.
Do these exercises include model answers?
Yes. Each interview question gives you several possible responses and asks you to pick the one that communicates most clearly and completely — the explanation then breaks down exactly why that answer works, including the specific vocabulary a strong candidate would use.
What if I choose an answer that isn't the strongest one?
You'll see which option was correct and read a full explanation of why it's stronger than the alternatives, plus the key vocabulary and phrasing worth reusing in a real interview.
Can I retry the questions?
Yes — use the "Try again" button on the results screen to reset and go through the set again.
Is this the same as a real technical or behavioural interview?
No — it's focused practice for the language side of interviewing: recognising which phrasing sounds precise and confident versus vague, and knowing the vocabulary interviewers expect for this role. It won't replace mock interviews, but it builds the vocabulary you'll need in one.
Where can I find interview prep for other roles?
Browse the full Interview exercises hub for 170+ modules covering behavioural, technical, and system design rounds across dozens of IT roles, or check the "Next up" link below to continue.
Do I need an account, and is my progress saved?
No account is needed. Progress is tracked only for your current visit — reloading or leaving the page resets the counter.
Who writes these interview questions?
Every question is written by the CoderSlingo team based on real technical interview patterns for this role, then reviewed for accuracy and clarity.