下面上面筋：
先问了一些之前intern的情况，然后介绍面试的背景是marketplace
SQL: date|session id|user id| event, calculate the average number of sessions/user per day for the last 30 days
analytics (Case)
Market Place want to add a new feature, add a sell button on the top when enter market place
Why we want to build this feature?
What Metric we need to measure this?
How to test?
Use the number of message sent to sellers/sessions to measure, the number decreased 10%
Why?
How would you measure it and test it?
What could we do?
select user_id, count(distinct session_id)/31
from table
group by user_id
where to_days(date) BETWEEN to_days(CURDATE()) AND BETWEEN to_days(CURDATE())-30
Why we want to build this feature?
non-stop way to boost the key metrics: have more people sign up as sellers and have more items on sale
What Metric we need to measure this?
sign-up rate and number of posted items
How to test?
A/B testing
Why?
more sellers and things to sell, so average decreases, not necessarily bad, or new competitors in the market
How would you measure it and test it?
measure the total number of messages and compare if it is same as before
What could we do?