I have two tables from different years, 2015 and 2016. Both tables have three columns as exampled below in table\_2015:

```
customer_id || plan_type || most_recent_date

110 || monthly || 2015/10/01

111 || weekly || 2015/11/07

```

I want to see how many people had the same plan type between the years and how many people switched plan types. How do I go about doing this?