Write a query to find conversion rate from orders
Last updated: November 16, 2025
Quick Overview
Write a SQL query to calculate conversion rate from the orders table, considering nulls and duplicates.
Vercel
November 16, 2025118
5
4,200 solved
Write a SQL query to calculate conversion rate from the orders table, considering nulls and duplicates.
Vercel asks this during the Phone Screen because data engineering skills are critical for the role. You should be comfortable with complex joins, window functions, CTEs, and performance optimization.
What the Interviewer Expects
- Use advanced SQL features: window functions, CTEs, subqueries
- Write efficient queries that avoid common performance pitfalls
- Handle complex data transformations with multiple joins and aggregations
- Discuss indexing strategy and query optimization
- Address data quality issues: duplicates, missing values, outliers
Key Topics to Cover
How to Approach This
- Clarify the schema and expected output format before writing queries.
- Use CTEs (WITH clauses) to break complex queries into readable steps.
- Consider window functions (ROW_NUMBER, RANK, LAG, LEAD) for ranking and sequential analysis.
- Watch for NULLs, duplicates, and edge cases in JOINs and GROUP BY.
- For pandas, prefer vectorized operations over row-by-row iteration.
Possible Follow-up Questions
- How would you optimize this query for a table with 100 million rows?
- What would you do if this query needs to run every 5 minutes?
- How would you handle slowly changing dimensions in this scenario?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to calculate the conversion rate from the orders table. The conversion rate is generally defined as the number of successful orders divided by the total number of unique visitors (or ses...
Approach
- Identify Unique Visitors: First, we need to determine the number of unique users or sessions that visited the site within the same time frame that we are measuring orders.
- **Count Successful...
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