I´m working on the Page Visits Funnel project, doing research for Cool T-shirts :
There´s something I just don´t understand, and I feel I´m not totally getting the differences between the types of join.
There´s four tables to work with: visits, cart, checkout and purchase. The goal is to calculate how many users abandon the purchasing process at each step.
We first take the “visits” table and there are 2000 rows there, i.e. 2000 instances of someone visiting the website. However, when I perform a left join with “cart”, I see that the visits_time column in the resulting table has swelled to 2052. How is this possible? If I´m not mistaken, what I´m getting with this left join is a column with all the visit times and another with the cart times. In the latter, there are many null entries, i.e. all those who visited the website but did not proceed to the cart. This seems pretty easy to understand, but I still can´t see what those 52 extra entries at visit times are. Where do they come from?
I feel I´m missing something quite obvious here, would appreciate if someone helped me with this