Calculate and Find Average Contacts and Sync Percentage

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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 Technical Screen rounds at PayPal.

Q: What role is this question designed for?

This question is commonly asked for Data Scientist candidates at PayPal during technical interviews.

Question

dw_peers

+--------------+---------------+-------------+
| user_id      | synced_contact| date_synced |
+--------------+---------------+-------------+
| 2589654316571| 4359086122    | 2023-02-01  |
| 1111111111111| 9999999999    | 2023-02-03  |
| 1111111111111| 8888888888    | 2023-02-03  |
| 2222222222222| 5555555555    | 2023-02-10  |
+--------------+---------------+-------------+

​

dw_users

+--------------+--------------+
| user_id      | phone_number |
+--------------+--------------+
| 2589654316571| 2349087633   |
| 1111111111111| 7777777777   |
| 2222222222222| 6666666666   |
| 3333333333333| 4444444444   |
+--------------+--------------+

##### Scenario

PayPal allows users to opt-in to sync their phone contacts. Contacts are stored in dw_peers; basic user info is stored in dw_users.

##### Question

Write SQL to calculate the average number of contacts synced per user. Write SQL to find the percentage of all PayPal users who have synced at least one contact.

##### Hints

Use aggregation on dw_peers, left-join to dw_users for denominator; COUNT(DISTINCT user_id) may help.

PracHub · Accepted Answer

This question evaluates proficiency in data aggregation, deduplication, and relational joins for computing user-level metrics such as average synced contacts and the percentage of users with at least one synced contact.

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