Pivot transactions by date without date libs

Q: How do I practice SQL interview questions?

PracHub provides an interactive SQL console where you can write and test queries against real database schemas. Get instant feedback and compare your solution with the expected output.

Q: What difficulty level is this coding question?

This is a medium difficulty Data Manipulation (SQL/Python) question, commonly asked during Onsite rounds at Instacart.

Q: What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Instacart during technical interviews.

Question

Given a stream of transaction rows (shopper_id, date_str, amount) where date_str is ISO format 'YYYY-MM-DD', produce a pivoted report for a specified 7‑day window [start_date, end_date]. For each shopper_id, output one row with columns shopper_id, d0, d1, ..., d6 where di is the sum of amount on the i‑th day offset from start_date. Constraints: rows may be unsorted and duplicate; you cannot import date/time libraries—treat date_str lexicographically for ordering and use simple arithmetic over precomputed consecutive ISO strings; assume all dates in the window exist. Specify your data structures, handling of missing days (fill with
0), and time/space complexity. Implement in any language.

PracHub · Accepted Answer

This question evaluates proficiency in data manipulation, string-based date handling, aggregation and pivot transformations, along with reasoning about data structures, de-duplication and missing-value filling.

Quick Overview

Pivot transactions by date without date libs