Simplified example: Two tables - people and times. Goal is to keep track of all the times a person walks through a doorway. 

A person could have between 0 and 50 entries in the times table daily. 

What is the proper and most efficient way to keep track of these records? Is it

```
times table
-----------
person_id
timestamp

```

I'm worried that this table can get well over a million records rather quickly. Insertion and retrieval times are of utmost importance. 

ALSO: Obviously non-normalized but would it be a better idea to do

```
times table
-----------
person_id
serialized_timestamps_for_the_day
date

```

We need to access each individual timestamp for the person but ONLY query records on date or the person's id.