We define as power users those users who bought at least 10 products. Write a query that returns for each user on which day they became a power user. That is, for each user, on which day they bought the 10th item.

The table below represents transactions. That is, each row means that the corresponding user has bought something on that date.


You can download the data set here.

Column Name Value Description
user_id 675 this is id of the user
date 2014-12-31 16:16:12 user 675 bought something on Dec 31, 2014 at 4:16:12 PM


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