Salesforce Data Engineering Interview Questions

The SQL problem you've described involves calculating the user retention rate based on a defined cohort. Let's break down how to approach this step-by-step, ensuring we understand each part clearly.

Step 1: Define the Cohort

Firstly, let's define what a "cohort" is in this context:

• A cohort consists of users who first logged into an application on a specific date or within a specific time period (e.g., week).

To find the cohort for each user, we need to determine their earliest login date. This can be done using MIN(login_date) GROUP BY user_id.

sql
 
1WITH user_cohorts AS (
2    SELECT 
3        user_id,
4        MIN(login_date) AS first_login,
5        DATE_TRUNC('week', MIN(login_date))::date AS week_cohort
6    FROM logins
7    GROUP BY user_id
8)
9SELECT * FROM user_cohorts;

This query creates a Common Table Expression (CTE) named user_cohorts that contains each user's earliest login date and the corresponding week cohort.

Step 2: Calculate Retained Users

Next, we need to identify which users from our defined cohorts returned within

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