# Distinct Product Categories > A quick category inventory. Canonical URL: Domain: SQL · Difficulty: easy · Seniority: L3 ## Problem The merchandising team is mapping out the full product taxonomy. Pull a deduplicated list of every product category currently in the catalog. ## Worked solution and explanation ### Why this problem exists in real interviews This is a simple DISTINCT query. It screens for the most basic deduplication operation in SQL. --- ### Break down the requirements #### Step 1: Deduplicate categories `SELECT DISTINCT category` returns unique category values. --- ### The solution **Simple deduplication** ```sql SELECT DISTINCT category FROM products ``` > **Cost Analysis** > > Scan of 15K rows. Trivially fast. > **Interviewers Watch For** > > Whether the candidate keeps it simple. This is a one-statement query. > **Common Pitfall** > > Using GROUP BY category without any aggregates is equivalent but less semantically clear for this use case. DISTINCT is idiomatic for simple deduplication. --- ## Common follow-up questions - When would GROUP BY be preferred over DISTINCT? _(When you also need aggregates like COUNT or SUM.)_ - What if category has NULLs? _(NULL appears as a distinct value. Tests whether to filter it.)_ - How would you sort the categories alphabetically? _(Add ORDER BY category.)_ ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/distinct_product_categories) - [SQL Interview Questions](https://datadriven.io/sql-interview-questions) - [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep) - [Daily Challenge](https://datadriven.io/daily) --- Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.