Real Data Science SQL Interview Questions and Answers # 1 | Data Science Interview Questions - YouTube

 https://www.youtube.com/watch?v=Td-cmLfQ7uU&ab_channel=TinaHuang

 01:40

building a potential and reasonable schema

 02:28

-- is a comment in SQL

 03:06

FROM -> JOIN -> ON … AND

 04:21

line 13: build a function by using SELECT

 04:34

COUNT (DISTINCT …)

1. joining all iOS and web users by ID
2. func DATE_TRUNC
3. num_users = distinct count by 'day'
4. group the result into num_users and day

CREATE TABLE

INSERT INTO
VALUES
(now()), INTERVAL (time)