Clarify the table schema and confirm that session duration is stored in seconds. Then write a SQL query that filters sessions with duration > 180 seconds and computes the average duration using AVG, ensuring proper handling of NULLs and data types.
Pro tip: Mention that you would check for edge cases like sessions exactly 3 minutes (180 seconds) and decide whether to use > or >= based on business definition. Also, consider if the average should be computed on filtered rows only or if you need to handle missing data.
Restate the problem: find the average session length for sessions longer than 3 minutes. Confirm that 3 minutes equals 180 seconds and that 'longer than' means strictly greater than 180.
Assume a table named 'sessions' with columns 'session_id', 'country', 'duration_seconds'. Clarify if there are any other relevant columns or if the table name is different.
Use a SELECT statement with AVG(duration_seconds) and a WHERE clause filtering duration_seconds > 180. Optionally, group by country if the question implies per-country averages, but the question asks for overall average.
Discuss handling of NULL durations, ensuring the column is numeric, and potential indexing on duration_seconds for performance. Also, consider if the average should be rounded or formatted.
Walk through the query logic, explain the filter and aggregation, and mention how you would test it with sample data or edge cases like exactly 180 seconds.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
First, compute the duration of each session by subtracting the start time from the end time. Then, bucket the durations into 5-minute intervals using integer division or a floor function, and finally group by the bucket to count the number of sessions in each bin.
Pro tip: Clarify whether the bins should be labeled by the lower bound (e.g., '0-5 min') or by the bin index, and mention that you'd handle edge cases like sessions exactly on a boundary consistently. Also, consider if you need to include empty bins with zero counts for a complete histogram.
Use the session end time minus start time to get the duration in a consistent unit, such as seconds or minutes. Ensure you handle any NULL or invalid timestamps appropriately.
Decide that each bin represents a 5-minute interval. Determine how to assign sessions to bins, e.g., using floor(duration_minutes / 5) to get the bin index.
Compute the bin index or label for each session based on its duration. For example, bin_index = FLOOR(duration_seconds / 300) or bin_label = CONCAT(FLOOR(duration_minutes/5)*5, '-', FLOOR(duration_minutes/5)*5+5, ' min').
Group by the bin index or label and count the number of sessions in each group. Use COUNT(*) or COUNT(session_id).
Select the bin column and the count column, and order by bin to present the histogram in ascending order. Optionally, include bins with zero counts by left joining with a generated series of bins.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
First, aggregate the sessions table to get total sessions per country. Then, perform a self-join on the aggregated table where the session counts are within 10% of each other, ensuring each pair is listed once with countries in separate columns. Use a condition like `a.sessions BETWEEN 0.9 * b.sessions AND 1.1 * b.sessions` and `a.country < b.country` to avoid duplicates and self-pairs.
Pro tip: Clarify whether 'within 10%' means 10% of the smaller value or the larger value; in practice, using a symmetric range (e.g., between 90% and 110% of the other) is common, but confirm with the interviewer to avoid ambiguity.
Write a subquery or CTE that groups the sessions table by country and counts the number of sessions for each country.
Join the aggregated table to itself, applying the condition that the session counts are within 10% of each other.
Add a condition like `a.country < b.country` to ensure each pair appears only once and no country is paired with itself.
Output the two country columns, aliasing them appropriately (e.g., country1, country2).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.