(BigQuery) SQL Truisms:

1. What is the smallest common denominator in the table? This is the primary key, which is abstracted away in BigQuery.
2. You can only ever work on one row of data. This means that the thing you access in the select is on a row level. So to do whatever you want to do, you need to get all the pieces in the same row.
3. You can do anything with SQL. Except (dynamically) add new columns
4. You can use scripts. Use JSON like it is no one's business in BigQuery