Data Analyst question bank
100 questions. Filter by level and skill, track what you've solved, and see how many people get each one right.
- WHERE vs HAVING
- Mean or median for salaries
- Which join keeps all customers
- COUNT(*) vs COUNT(column)
- Best chart for a trend
- What a pivot table does
- Finding NULL values
- Correlation and causation
- COUNT(DISTINCT) with NULLs
- Rows from an INNER JOIN
- UNION vs UNION ALL
- AVG with a NULL value
- Bucketing with CASE WHEN
- Dividing two integers in SQL
- Why this GROUP BY fails
- Does BETWEEN include the ends
- Matching text with LIKE
- Top seller with ORDER BY and LIMIT
- Absolute references in Excel
- VLOOKUP returns wrong prices
- SUMIFS with two conditions
- Median of an even-sized list
- Percent change up and down
- Percentage points vs percent
- Calculating monthly churn
- Overall funnel conversion
- Chart for 12 product categories
- Lost leading zeros in IDs
- Counting missing values in pandas
- Total sales per city in pandas
- Type of a 1 to 5 rating
- Dimensions vs measures
- Which set has more spread
- What a primary key guarantees
- Revenue doubled after a join
- Latest order per customer
- Running total of sales
- What a p-value means
- Reading a cohort retention table
- Calculating conversion rate
- Filling missing income values
- Designing an executive dashboard
- LEFT JOIN that lost customers
- RANK vs DENSE_RANK after a tie
- Month-over-month change with LAG
- Share of paid orders in one query
- Customers who never ordered
- Grouping orders by month
- Counting repeat customers with a CTE
- Looking up a value to the left
- Share of sales in a pivot table
- Pivot ignores new data rows
- Same cleaning every Monday
- Measure or calculated column
- Outlier cutoff with the IQR rule
- Average price across two stores
- Reading a 95% confidence interval
- False positive in an A/B test
- Relative lift of a variant
- Rows after a pandas left merge
- Month 2 retention for a cohort
- ARPU vs ARPPU
- Bar chart that exaggerates
- Why use a 7-day moving average
- Report total does not match finance
- Z-score of a branch
- Shaping a Power BI model
- SUM over zero matching rows
- Overall rate goes the other way
- Stopping a test early
- NOT IN returns nothing
- Detecting a small lift
- Average of averages
- Only looking at active customers
- Daily numbers do not match
- A metric that can be gamed
- Running total with tied dates
- Filter inside the ON clause
- Not-equal filter loses rows
- PERCENTILE_CONT vs PERCENTILE_DISC
- NTILE with 10 rows
- Latest order changes between runs
- Click-through rate with zero impressions
- Adding up daily active users
- How reliable is a fraud flag
- Uneven groups in a 50/50 test
- Lift that fades after week one
- Randomised by user, analysed by session
- Halving the margin of error
- Worst stores improved on their own
- Correlation near zero
- Feature users retain better
- Total row is less than the sum
- FIXED LOD ignores a filter
- Grand total of an average pivot
- Filtering NaN with == in pandas
- Combining two store medians
- Comparing a week to last year
- East sales on the West row
- GROUP BY with NULL cities