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Data Analytics Interview Questions in Mumbai

36 practice questions with answers for Data Analytics interviews in Mumbai.

Data Analytics jobs in Mumbai

Mumbai is India's financial capital, so banks, fintechs, insurers, media and consulting firms drive much of the hiring. Data and QA interviews often include domain questions on payments, risk, trading or customer analytics.

Below are 36 questions that match the mix of service, product and domain employers hiring data analysts in Mumbai.

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A stakeholder says the Power BI report shows different revenue than their Excel file. How do you troubleshoot?

Power BIMedium

Show answer

I would first agree on definitions: gross or net, including tax or returns, order date or invoice date. Then compare one small slice, such as one month and one region, in both. I check filters on the report and page, relationships that drop unmatched rows, refresh time versus the Excel extract time, and duplicate rows. Once the gap is explained, I document the definition in the report so the question does not repeat.

Marketing wants to A/B test two email subject lines on a list of 2,000 subscribers. What do you advise?

A/B Testing & ExperimentsMedium

Show answer

With 1,000 per group and a typical click rate of 3%, only a very large difference, roughly 70% relative or more, would be detectable, so a small real lift would look like noise. I would suggest testing on a larger send, pooling several campaigns, or using open-to-click rate with a bigger effect. If they still run it, report the confidence interval and treat the result as directional.

How do you create a dual-axis chart in Tableau, for example sales bars with a profit margin line?

TableauEasy

Show answer

Drag Order Date to Columns as a continuous or discrete month, put Sales on Rows, then drag Profit Ratio to Rows next to it. Right-click the second pill and choose Dual Axis. On the Marks card set Sales to Bar and Profit Ratio to Line. Decide whether to synchronise axes: do not synchronise when units differ, like rupees and percentage. Label the axes clearly so readers know which is which.

How do you calculate a simple customer lifetime value?

Statistics and Case StudiesHard

Show answer

A simple formula is CLV = average order value x purchase frequency per year x gross margin x expected lifetime in years. Example: 800 rupees x 6 orders x 30 percent margin x 3 years = 4,320 rupees. Expected lifetime can be estimated as 1 divided by annual churn rate. A better version discounts future value and calculates CLV by cohort or segment, because averages hide very different customer groups.

Write Python code to calculate the sample size per group for a conversion test with a 4% baseline and a 10% relative lift.

A/B Testing & ExperimentsMedium

Show answer

from statsmodels.stats.power import NormalIndPower from statsmodels.stats.proportion import proportion_effectsize baseline = 0.04 target = baseline * 1.10 # 4.4% effect = proportion_effectsize(target, baseline) n = NormalIndPower().solve_power( effect_size=effect, alpha=0.05, power=0.8, alternative='two-sided' ) print(round(n)) # roughly 39,000 users per group

Write SQL using LAG to compare each month's revenue with the previous month.

SQLMedium

Show answer

WITH monthly AS ( SELECT DATE_TRUNC('month', order_date) AS month, SUM(amount) AS revenue FROM orders GROUP BY 1 ) SELECT month, revenue, LAG(revenue) OVER (ORDER BY month) AS prev_revenue, ROUND(100.0 * (revenue - LAG(revenue) OVER (ORDER BY month)) / NULLIF(LAG(revenue) OVER (ORDER BY month), 0), 1) AS mom_pct FROM monthly ORDER BY month;

You share a forecasting workbook and users keep overwriting formulas. How do you protect it?

ExcelMedium

Show answer

Separate input cells from calculation cells and colour inputs clearly. Unlock only the input cells through Format Cells, Protection, then protect the sheet so formulas cannot be edited, and optionally hide formulas. Add data validation on inputs to block wrong values such as negative quantities. Protect workbook structure so sheets cannot be deleted, keep a version history, and add a short instructions sheet so users know where to type.

Write pandas code to compute month-on-month percentage change and cumulative sales for each store.

Python for AnalysisMedium

Show answer

df = df.sort_values(['store', 'month']) df['mom_pct'] = ( df.groupby('store')['sales'].pct_change() * 100 ).round(1) df['cum_sales'] = df.groupby('store')['sales'].cumsum() # first month of each store has NaN for mom_pct, which is expected

What are parameters in Tableau and how do you use them?

TableauMedium

Show answer

A parameter is a single user-controlled value, such as a number, date or string, that is independent of the data. On its own it does nothing; you reference it in calculations, filters, reference lines or bins. Common uses are a Top N selector, a what-if growth rate, or a measure switcher where a CASE statement picks Sales, Profit or Quantity based on the parameter. Parameter actions let users set it by clicking a mark.

What are bookmarks and drill-through in Power BI?

Power BIMedium

Show answer

Bookmarks save a report view state for navigation; drill-through jumps to a detail page filtered to the item you picked.

What is the difference between OLTP and OLAP systems?

Data Modelling & WarehousingEasy

Show answer

OLTP systems run day-to-day operations, such as billing or order entry. They handle many small inserts and updates, use normalised tables and need fast single-row access. OLAP systems support analysis, scanning millions of rows to aggregate sales by month or region. They use denormalised star schemas, columnar storage and are mostly read-heavy. Analysts should query OLAP copies so heavy reports do not slow down the live application.

What is the difference between relationships, joins and data blending in Tableau?

TableauMedium

Show answer

Relationships, the default logical layer, connect tables flexibly and Tableau decides join type and level per view, avoiding duplicated measures. Joins physically merge tables into one at a fixed level, which can duplicate rows if grains differ. Blending combines data from separate data sources at the view level using a primary and secondary source, aggregating the secondary first. Prefer relationships, use joins for specific row-level needs, and blending as a last resort.

Write SQL to find the first-touch and last-touch channel for every user who converted.

Web & Marketing AnalyticsMedium

Show answer

WITH touches AS ( SELECT t.user_id, t.channel, t.touch_ts, ROW_NUMBER() OVER (PARTITION BY t.user_id ORDER BY t.touch_ts) AS first_rank, ROW_NUMBER() OVER (PARTITION BY t.user_id ORDER BY t.touch_ts DESC) AS last_rank FROM marketing_touches t JOIN conversions c ON c.user_id = t.user_id AND t.touch_ts <= c.converted_ts ) SELECT user_id, MAX(CASE WHEN first_rank = 1 THEN channel END) AS first_touch, MAX(CASE WHEN last_rank = 1 THEN channel END) AS last_touch FROM touches GROUP BY user_id;

What is the difference between COUNT, COUNTA and COUNTIF?

ExcelEasy

Show answer

COUNT counts numbers, COUNTA counts non-empty cells and COUNTIF counts cells meeting one condition; COUNTIFS handles several conditions.

Email open rates suddenly jumped from 22% to 45% without any campaign change. Should you celebrate?

Web & Marketing AnalyticsMedium

Show answer

No. Privacy features in some mail apps pre-load email images, which fires the open tracking pixel even if the person never reads the email, so open rates get inflated. Check opens by email client to confirm. Move reporting towards clicks, click-to-send rate, conversions and unsubscribes, which reflect real behaviour, and avoid using opens alone to pick winning subject lines or to define engaged subscribers.

Your NOT IN query unexpectedly returns zero rows. Why might that happen, and how do EXISTS and IN differ?

SQLMedium

Show answer

IN checks whether a value is in a list or subquery result; EXISTS checks whether a subquery returns at least one row and stops at the first match. Results are the same in most cases, and modern optimisers often run them similarly. The big difference is NOT IN with NULLs: if the subquery returns any NULL, NOT IN returns no rows. NOT EXISTS behaves correctly, so prefer it for anti-joins.

Explain row context and filter context.

Power BIMedium

Show answer

Row context evaluates one row at a time (calculated columns); filter context is the set of filters from slicers, visuals and relationships that a measure sees.

Tell me about a time you found a serious data quality issue.

Data CleaningMedium

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Situation: while building a returns report I noticed one warehouse had zero returns for three months. Task: confirm whether it was real. Action: I compared with the source system and found its return codes had changed after a software update, so my filter missed them. I informed the data owner, updated the mapping and back-filled the history. Result: the corrected report showed that warehouse had the highest return rate, which led to a packaging review.

Write a CREATE TABLE statement for a sales fact table linked to date, product and store dimensions.

Data Modelling & WarehousingEasy

Show answer

CREATE TABLE fact_sales ( date_key INT NOT NULL REFERENCES dim_date(date_key), product_key INT NOT NULL REFERENCES dim_product(product_key), store_key INT NOT NULL REFERENCES dim_store(store_key), invoice_no VARCHAR(20) NOT NULL, -- degenerate dimension quantity INT NOT NULL, net_amount DECIMAL(12,2) NOT NULL, discount_amount DECIMAL(12,2) DEFAULT 0 );

Write SQL to show each category's percentage share of total revenue.

SQLMedium

Show answer

SELECT category, SUM(amount) AS revenue, ROUND(100.0 * SUM(amount) / SUM(SUM(amount)) OVER (), 2) AS pct_share FROM sales GROUP BY category ORDER BY revenue DESC; -- SUM(SUM(amount)) OVER () is the grand total across all groups

How would you reconcile two large lists in Excel?

ExcelHard

Show answer

Use XLOOKUP or COUNTIF to flag missing items in each list, or merge them in Power Query with a full outer join and filter unmatched rows.

How would you automate a weekly report with Python?

Python for AnalysisHard

Show answer

Pull data with SQL or APIs, clean and aggregate with Pandas, build charts and an Excel or PDF output, and schedule it with cron or Airflow with logging and alerts.

What is the difference between mean and median for reporting salaries?

Statistics and Case StudiesMedium

Show answer

Salaries are right-skewed, so the median better represents the typical employee while the mean is pulled up by a few high earners.

A stakeholder asks for a pie chart of 12 product categories. When is a pie chart acceptable, and what would you suggest?

Data StorytellingEasy

Show answer

A pie chart works only for showing parts of a whole with very few categories, two to four, where one share clearly dominates, such as 70 percent of orders are prepaid. Avoid it when there are many slices, when values are close, or when comparing across periods, because people judge angles poorly. A sorted bar chart is almost always easier to read and compare. Never use 3D pies.

What types of dashboard actions does Tableau offer?

TableauMedium

Show answer

Filter actions filter other sheets when a user selects or hovers on a mark, such as clicking a region to filter a product table. Highlight actions emphasise related marks without removing others. URL actions open a web page with field values in the link. Go to Sheet navigates to another dashboard. Parameter and set actions update a parameter or set based on selection, enabling advanced interactions like dynamic drill-downs and comparisons.

Write pandas code to standardise inconsistent city names such as 'delhi ', 'New Delhi' and 'DELHI'.

Data CleaningMedium

Show answer

city_map = { 'delhi': 'Delhi', 'new delhi': 'Delhi', 'bombay': 'Mumbai', 'mumbai': 'Mumbai', 'bengaluru': 'Bengaluru', 'bangalore': 'Bengaluru', } clean = df['city'].str.strip().str.lower().str.replace(r'\s+', ' ', regex=True) df['city_clean'] = clean.map(city_map).fillna(clean.str.title()) print(df['city_clean'].value_counts())

Write a UTM-tagged URL for a paid Instagram campaign promoting a summer sale, and give two naming rules.

Web & Marketing AnalyticsEasy

Show answer

https://www.example.com/sale?utm_source=instagram&utm_medium=paid_social&utm_campaign=summer_sale_2026&utm_content=reel_video_a -- Rule 1: always lower case with underscores; 'Instagram' and 'instagram' become separate rows -- Rule 2: keep a shared UTM sheet with allowed source and medium values so every team tags the same way

What is the difference between marketing mix modelling and multi-touch attribution?

Web & Marketing AnalyticsHard

Show answer

Multi-touch attribution tracks individual user journeys and assigns credit to clicks and views, but it misses offline channels like TV and outdoor, and it is weakened by cookie loss and privacy rules. Marketing mix modelling uses aggregated weekly data, such as spend per channel, sales, price and seasonality, in a regression to estimate each channel's contribution and diminishing returns. MMM is better for budget planning; MTA is better for quick digital optimisation.

Explain Matplotlib vs Seaborn.

Python for AnalysisMedium

Show answer

Matplotlib is the low-level plotting library with full control; Seaborn builds on it with attractive statistical charts and simpler syntax.

Tell me about a time you used data to challenge an assumption.

Statistics and Case StudiesMedium

Show answer

Situation: our team believed weekend discounts drove most sales. Task: I was preparing the monthly review. Action: I compared discount and non-discount weekends over six months and controlled for paydays and festivals. Discounts moved sales forward from the following week but added little overall. I presented it with one clear chart. Result: management trialled fewer discount weekends, and margin improved without a fall in monthly revenue.

Write a DAX measure for year-over-year sales growth percentage.

Power BIMedium

Show answer

Sales LY = CALCULATE([Total Sales], SAMEPERIODLASTYEAR('Date'[Date])) Sales YoY % = VAR cur = [Total Sales] VAR prev = [Sales LY] RETURN DIVIDE(cur - prev, prev) -- needs a marked date table; format the measure as a percentage

How do you handle large CSV files that do not fit in memory in Python?

Python for AnalysisMedium

Show answer

Read in chunks with chunksize, load only needed columns, set efficient dtypes or switch to Dask, Polars or a database.

What is normalisation?

SQLMedium

Show answer

Organising tables to reduce redundancy and anomalies by splitting data into related tables, commonly up to third normal form.

How do you find duplicate rows in a table?

SQLMedium

Show answer

SELECT col, COUNT(*) FROM t GROUP BY col HAVING COUNT(*) > 1; use ROW_NUMBER() partitioned by the key to delete extras.

How do you merge two DataFrames on different column names?

Python for AnalysisMedium

Show answer

pd.merge(df1, df2, left_on='cust_id', right_on='id', how='left') joins on differently named keys.

What is dimensional modelling?

Data Modelling & WarehousingEasy

Show answer

Dimensional modelling is a way of designing analytical tables around business processes. Numeric events such as sales or payments go into fact tables, and descriptive context such as customer, product, store and date goes into dimension tables. The design is easy for business users to understand and fast for BI tools to aggregate. For example, a retail model might have one sales fact joined to date, product, store and customer dimensions.

Companies with offices in Mumbai (51)

IT services

TCS

Data Analytics interview questions

40 questions
4 rounds

Mumbai, Chennai, Pune +2

Data Analytics Interview Questions in Mumbai

Data Analytics jobs in Mumbai

A stakeholder says the Power BI report shows different revenue than their Excel file. How do you troubleshoot?

Marketing wants to A/B test two email subject lines on a list of 2,000 subscribers. What do you advise?

How do you create a dual-axis chart in Tableau, for example sales bars with a profit margin line?

How do you calculate a simple customer lifetime value?

Write Python code to calculate the sample size per group for a conversion test with a 4% baseline and a 10% relative lift.

Write SQL using LAG to compare each month's revenue with the previous month.

You share a forecasting workbook and users keep overwriting formulas. How do you protect it?

Write pandas code to compute month-on-month percentage change and cumulative sales for each store.

What are parameters in Tableau and how do you use them?

What are bookmarks and drill-through in Power BI?

What is the difference between OLTP and OLAP systems?

What is the difference between relationships, joins and data blending in Tableau?

Write SQL to find the first-touch and last-touch channel for every user who converted.

What is the difference between COUNT, COUNTA and COUNTIF?

Email open rates suddenly jumped from 22% to 45% without any campaign change. Should you celebrate?

Your NOT IN query unexpectedly returns zero rows. Why might that happen, and how do EXISTS and IN differ?

Explain row context and filter context.

Tell me about a time you found a serious data quality issue.

Write a CREATE TABLE statement for a sales fact table linked to date, product and store dimensions.

Write SQL to show each category's percentage share of total revenue.

How would you reconcile two large lists in Excel?

How would you automate a weekly report with Python?

What is the difference between mean and median for reporting salaries?

A stakeholder asks for a pie chart of 12 product categories. When is a pie chart acceptable, and what would you suggest?

What types of dashboard actions does Tableau offer?

Write pandas code to standardise inconsistent city names such as 'delhi ', 'New Delhi' and 'DELHI'.

Write a UTM-tagged URL for a paid Instagram campaign promoting a summer sale, and give two naming rules.

What is the difference between marketing mix modelling and multi-touch attribution?

Explain Matplotlib vs Seaborn.

Tell me about a time you used data to challenge an assumption.

Write a DAX measure for year-over-year sales growth percentage.

How do you handle large CSV files that do not fit in memory in Python?

What is normalisation?

How do you find duplicate rows in a table?

How do you merge two DataFrames on different column names?

What is dimensional modelling?

Companies with offices in Mumbai (51)

TCS

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