**System Design: Design a Data Warehouse**\nImagine you are tasked with designing a data warehouse for a retail company that wishes to analyze sales information, customer behaviors, and inventory data. Discuss how would you structure the data warehouse, what kind of data model you would implement, the types of data sources you would consider, and how you would ensure the system scales with the business's growth. Be prepared to address considerations around ETL processes and querying capabilities.

**LeetCode #15 - 3Sum**\nGiven an array of integers, find all the unique triplets (a, b, c) such that a + b + c = 0, where a, b, and c are distinct indices in the array. You must return the result in a specific order of triplets.\n\n**Example 1:**\nInput: `[-1, 0, 1, 2, -1, -4]`\nOutput: `[[-1, -1, 2], [-1, 0, 1]]`\nExplanation: `-1 + -1 + 2 = 0` and `-1 + 0 + 1 = 0` are the two unique triplets.\n\n**Example 2:**\nInput: `[0, 1, 1]`\nOutput: `[]`\nExplanation: No triplet exists that sums to zero.\n\n**Constraints:**\n- 0 <= nums.length <= 3000\n- -10^5 <= nums[i] <= 10^5\n

**Design a Data Warehouse Schema**\nYou are tasked with designing a data warehouse schema for an online retail company that needs to analyze customer behavior. The company wants to track user purchases, product categories, and sales over time. Describe the overall architecture, including the choice of databases, ETL processes, and data models you would use to achieve this. Discuss how data consistency and scalability can be maintained.\n