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SQL Managerial Round Questions & Answers

35 questions for the managerial round stage — 2 easy, 20 medium, 13 hard.

About the managerial round round

The managerial round is usually with a hiring manager or team lead. It mixes real-work scenarios, prioritisation and stakeholder questions with behavioural questions about ownership, conflict and learning.

Tips for the managerial round round

Use the STAR format for every story: Situation, Task, Action, Result.
Show trade-offs: what you chose, what you gave up and why.
Be honest about mistakes and focus on what you changed afterwards.
Ask the manager about team goals and how success is measured in the role.

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You need customers who bought both product A and product B. How would you write it?

JoinsMedium

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Group by customer and count distinct matching products: SELECT customer_id FROM order_items WHERE product_id IN ('A', 'B') GROUP BY customer_id HAVING COUNT(DISTINCT product_id) = 2. Alternatively use INTERSECT of two queries, or two EXISTS conditions. The HAVING approach is concise, scans the table once and is easy to extend to three or more products.

You need to delete duplicate rows but keep one copy of each. How do you do it?

Subqueries and CTEsMedium

Show answer

Use a CTE with ROW_NUMBER: WITH d AS (SELECT id, ROW_NUMBER() OVER (PARTITION BY email ORDER BY id) AS rn FROM users) DELETE FROM users WHERE id IN (SELECT id FROM d WHERE rn > 1). SQL Server allows DELETE FROM d WHERE rn > 1 directly. Back up the table first, run a SELECT to verify, then add a unique constraint to prevent new duplicates.

A query that ran in 1 second now takes 40 seconds after a data load. What do you check?

Indexes and PerformanceMedium

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Compare the current execution plan with the old one. A big data load often makes statistics stale, causing poor row estimates and a different join or scan choice, so update statistics first. Check for index fragmentation, missing indexes after the load, blocking from other sessions, and whether the data volume crossed a threshold. Test again after each change.

A recursive CTE on a category tree runs forever. What is the likely cause and fix?

Subqueries and CTEsHard

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The data probably has a cycle, such as category A as parent of B and B as parent of A, so recursion never ends. Add a depth column and stop at a maximum level, track a path string or array and exclude nodes already visited, and use database limits such as MAXRECURSION in SQL Server. Then fix the cyclic data at the source with constraints or validation.

Average order value looks too low in a report. What could be wrong?

Aggregation and GroupingMedium

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Check the grain: if the query averages order items instead of orders, each line counts separately and the average drops. Joins can also duplicate rows. Verify whether cancelled or zero-value orders are included and how NULL amounts are treated. Compute SUM(amount) / COUNT(DISTINCT order_id) at order level and compare with business definitions before changing the report.

Produce region subtotals and a grand total in one query.

Aggregation and GroupingMedium

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SELECT COALESCE(region, 'All Regions') AS region, COALESCE(city, 'Subtotal') AS city, SUM(sales) AS sales FROM store_sales GROUP BY ROLLUP(region, city) ORDER BY region, city; In MySQL use GROUP BY region, city WITH ROLLUP. Use GROUPING() to label totals when real NULLs exist.

A business user needs a dashboard on a complex 6-table join that runs slowly. Would you use a view or a materialised view?

Transactions and Advanced SQLMedium

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A normal view only simplifies the query; it still runs the full join every time, so performance does not improve. If the data can be a few minutes or hours old, a materialised view or summary table refreshed on schedule gives fast reads. If real-time data is required, tune the underlying query with indexes or build an incrementally maintained table.

An interviewer asks for the Nth highest salary in a reusable way. How do you answer?

Subqueries and CTEsMedium

Show answer

Use DENSE_RANK so ties share a rank: SELECT salary FROM (SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS r FROM employees) t WHERE r = :n. Alternatively use ORDER BY salary DESC with OFFSET n-1 ROWS FETCH NEXT 1 ROW ONLY on distinct salaries. Mention how ties are handled and that per-department versions add PARTITION BY department_id.

Describe a time you found and fixed a wrong number in a report.

JoinsMedium

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Situation: a monthly dashboard showed 30 percent higher revenue than finance figures. Task: find the cause before the leadership review. Action: I traced the SQL, found a join to the shipments table that duplicated orders with split shipments, rewrote it with a pre-aggregated CTE and reconciled totals with finance. Result: numbers matched exactly and I added a row-count test to the report pipeline.

A join between two large tables takes minutes. How would you speed it up?

JoinsHard

Show answer

Check the execution plan for scans, join type and row estimates. Ensure join keys have indexes and matching data types, because implicit conversion blocks index use. Filter both sides early, select only needed columns, update statistics, and avoid functions on join columns. For very large data, consider partitioning, pre-aggregated tables, or batch processing outside peak hours.

Tell me about a production incident involving a database and how you handled it.

Transactions and Advanced SQLMedium

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Situation: during a sale, order placement started failing with lock timeouts. Task: restore service quickly. Action: I identified a long-running reporting query holding locks on the orders table, coordinated with the team to kill it, and moved that report to the read replica. Result: orders recovered within ten minutes, and we added query timeouts and a rule that reports never run on the primary.

What are anti joins and semi joins?

JoinsMedium

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A semi join returns rows from the first table that have at least one match in the second, without duplicating them, usually written with EXISTS or IN. An anti join returns rows with no match, written with NOT EXISTS or LEFT JOIN with WHERE right.key IS NULL. For example, customers who never ordered is an anti join. They avoid duplicates that a normal join could create.

Your GROUP BY query returns an error that a column is not in the group by clause. How do you fix it?

Aggregation and GroupingMedium

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Each selected column must be grouped or aggregated. Decide what you need: add the column to GROUP BY if it defines the group, aggregate it with MIN, MAX or STRING_AGG if any or all values are acceptable, or remove it. If you need details of the top row in each group, use a window function such as ROW_NUMBER instead of GROUP BY.

A LEFT JOIN is returning fewer rows than the left table. Why could that happen?

JoinsMedium

Show answer

A LEFT JOIN never removes left rows by itself, so a WHERE condition on the right table is likely filtering out rows where it is NULL. For example WHERE o.status = 'Paid' drops customers without orders. Move the condition into the ON clause or add OR o.status IS NULL. Another cause is a later INNER JOIN in the chain that removes rows.

A report sums amounts stored in a FLOAT column and finance says totals are off by a few paise. Why?

SQL BasicsHard

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FLOAT stores approximate binary values, so decimals such as 0.1 cannot be represented exactly and rounding errors accumulate over millions of rows. Money should be stored as DECIMAL or NUMERIC with fixed scale, for example DECIMAL(12,2). Fix it by migrating the column type carefully, validating totals before and after, and rounding only at presentation time.

What is table partitioning and how does it help performance?

Indexes and PerformanceHard

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Partitioning splits a large table into smaller physical pieces by a key, such as range partitions by month, list partitions by region, or hash partitions. Queries filtering on the partition key read only relevant partitions, called partition pruning. It also makes maintenance easier, such as dropping old months instantly. It does not help queries that do not filter on the partition key.

A daily aggregation over 2 billion rows is too slow for a dashboard. What would you propose?

Aggregation and GroupingHard

Show answer

Avoid recalculating raw data on every request. Build a summary table or materialised view at daily grain refreshed incrementally, partition the fact table by date, and use columnar storage if available. Pre-compute common metrics, index the summary on dimensions used in filters, and let the dashboard query the summary. Validate summary totals against raw data periodically.

A query with many OR conditions across different columns is slow. How can you optimise it?

Indexes and PerformanceHard

Show answer

OR across different columns often prevents a single index seek. Rewrite it as UNION ALL of separate queries, each using its own index, removing duplicates carefully if needed, or use IN for multiple values of the same column. Some optimisers can combine indexes with bitmap or index merge plans. Compare plans and timings to choose the best approach.

Describe your SQL project from college or internship.

Window FunctionsEasy

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Situation: during my internship the team tracked student attendance in spreadsheets. Task: build a database and reports. Action: I designed tables for students, courses and attendance, loaded data, and wrote queries with joins, group by and window functions to show monthly attendance and low-attendance alerts. Result: faculty got a weekly report automatically, and I learned how real data quality issues affect queries.

How do you prevent SQL injection in applications?

Transactions and Advanced SQLMedium

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Never build SQL by concatenating user input. Use parameterised queries or prepared statements, where input is sent separately from the SQL text, or ORMs that do this automatically. Validate and whitelist inputs such as sort column names, give application users least privilege, and avoid dynamic SQL in procedures unless parameters are bound. Input like ' OR 1=1 -- then cannot change the query logic.

How do you explain a technical database issue to a non-technical manager?

Transactions and Advanced SQLMedium

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Situation: my manager asked why a report was late every Monday. Task: explain and get approval for a fix. Action: I compared the database to a busy shop counter where reports and customers queue together, showed the timing data, and proposed a separate reporting copy. Result: he understood the trade-off in five minutes, approved the read replica, and Monday reports became on time.

What is BCNF and how is it different from 3NF?

Database DesignHard

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Boyce-Codd Normal Form requires that for every functional dependency, the determinant is a candidate key. 3NF allows a dependency where the dependent attribute is part of a candidate key, while BCNF does not. For example, if a teacher teaches only one subject but a student-subject pair determines the teacher, the table is in 3NF but not BCNF and should be split.

What is denormalisation and when is it used?

Database DesignMedium

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Denormalisation intentionally adds redundancy, such as storing customer name in an orders reporting table, to reduce joins and speed up reads. It is common in data warehouses, reporting tables and high-read applications. The cost is extra storage and the need to keep copies consistent through ETL, triggers or application logic. Use it when read performance matters more than write simplicity.

Your running total jumps by large amounts on some dates instead of row by row. Why?

Window FunctionsMedium

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With ORDER BY and no explicit frame, the default frame is RANGE UNBOUNDED PRECEDING, which treats all rows with the same order value as peers and includes them together. When several rows share the same date, the running total adds them all at once. Specify ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, or add a unique tiebreaker to ORDER BY.

Design tables for students, courses and enrolments.

Database DesignEasy

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CREATE TABLE students ( student_id INT PRIMARY KEY, name VARCHAR(100) NOT NULL ); CREATE TABLE courses ( course_id INT PRIMARY KEY, title VARCHAR(100) NOT NULL ); CREATE TABLE enrolments ( student_id INT REFERENCES students(student_id), course_id INT REFERENCES courses(course_id), enrolled_on DATE, PRIMARY KEY (student_id, course_id) ); The junction table resolves the many-to-many relationship.

How would you design data archiving for a table growing by 10 million rows a month?

Transactions and Advanced SQLHard

Show answer

Partition the table by month so old partitions can be detached or moved to an archive table or cheaper storage without heavy deletes. Define a retention policy with business and compliance teams, for example 24 months online. Keep archived data queryable through a separate schema or warehouse, update indexes and statistics, and automate the process with monitoring and alerts.

How do you read an EXPLAIN ANALYZE output in PostgreSQL?

Indexes and PerformanceMedium

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EXPLAIN ANALYZE SELECT * FROM orders WHERE customer_id = 101; Read the tree from the innermost node outward. Check node types such as Seq Scan, Index Scan or Hash Join, compare estimated rows with actual rows, and look at actual time per node. Large estimate errors suggest stale statistics, and Seq Scan on a selective filter suggests a missing index.

Two systems store customer IDs differently, one as INT and one as VARCHAR with leading zeros. How do you join them?

JoinsHard

Show answer

Convert consistently, for example CAST(b.cust_code AS INT) = a.customer_id, but understand this prevents index use on b.cust_code and fails on non-numeric values. Better options are a computed or persisted column with the converted value and an index, or a mapping table built during ETL. Also validate unmatched rows to catch formatting issues such as spaces.

Tell me about a time you significantly improved query performance.

Indexes and PerformanceMedium

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Situation: a daily settlement report took 45 minutes and often missed its deadline. Task: bring it under ten minutes. Action: I studied the execution plan, replaced a non-SARGable date filter, added a composite covering index, pre-aggregated a large join in a temp table and updated statistics. Result: runtime dropped to six minutes, and the finance team received reports on time every day.

Product prices change often, but old orders must keep the price at the time of purchase. How do you design it?

Database DesignHard

Show answer

Store the unit price, discount and tax in order_items when the order is created instead of reading the current product price, so history is not affected by updates. Maintain a product_price_history table with effective_from and effective_to dates for analysis. Reports on past orders use order_items values, while catalogue pages use the current price.

How do you handle a situation where business users dispute your numbers?

Aggregation and GroupingHard

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Situation: a regional manager said my sales report undercounted his region. Task: resolve it with facts. Action: I shared the query logic and definitions, compared a sample of his records with the database, and found his team counted orders on booking date while the report used invoice date. Result: we agreed on invoice date with finance, documented it, and added the definition to the report.

Inserts into a heavily used table have become slow. What could be causing it?

Indexes and PerformanceHard

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Too many indexes increase write cost, so audit and remove unused ones. Random UUID primary keys cause page splits and fragmentation. Triggers, foreign key checks without indexes on child columns, lock contention from long transactions, and log disk bottlenecks also slow inserts. Use batch inserts, sequential keys, proper indexing of foreign keys and monitor waits to find the actual bottleneck.

Tell me about a database design decision you made and its outcome.

Database DesignMedium

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Situation: our app stored user preferences in a wide table with 60 nullable columns. Task: make it flexible for new settings. Action: I proposed a key-value preferences table with a JSON column for rarely used settings, kept frequently queried fields as columns, and wrote a migration. Result: new settings no longer needed schema changes and query speed for common fields stayed the same.

Finance asks for the count of customers whose total spend crossed 1 lakh in each city. How do you write it?

Aggregation and GroupingHard

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Aggregate in two levels. First compute total spend per customer and city in a CTE: SELECT city, customer_id, SUM(amount) AS spend FROM orders GROUP BY city, customer_id. Then in the outer query: SELECT city, COUNT(*) FROM cte WHERE spend > 100000 GROUP BY city. Trying to do it in one GROUP BY by city fails because the threshold applies to each customer, not each city.

Someone ran an UPDATE without WHERE on production. What would you do?

SQL BasicsMedium

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Stop further changes and inform the lead and DBA immediately. If the session is still in an open transaction, roll back. Otherwise, restore affected rows from the latest backup or point-in-time recovery to a separate database and update the production table from it, or use audit or history tables if available. Afterwards, add safeguards such as safe-update mode, reviews and restricted write access.

Frequently asked questions

What happens in the SQL managerial round round?

How do I clear the managerial round round?

Use the STAR format for every story: Situation, Task, Action, Result. Show trade-offs: what you chose, what you gave up and why. Be honest about mistakes and focus on what you changed afterwards.

Which round comes next?

A typical order is online assessment, telephonic screening, one or two technical rounds, a managerial round and HR. Use the other round pages to practise each stage.

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