I am attempting to solve the DataLemur problem here.
When I run my query to only take those matches from the left table I'm left with a table with a set of new columns. Now I want to query one of those new columns to identify those rows that are NULL.
I don't understand how to query this new joined table as it doesn't have a name. I've looked at other examples and am confused how they work.
My query:
SELECT *
FROM pages p
LEFT JOIN page_likes pl ON p.page_id = pl.page_id
Current output from my query:
| page_id | page_name | user_id | page_id | liked_date |
|---|---|---|---|---|
| 20001 | SQL Solutions | 111 | 20001 | 04/08/2022 00:00:00 |
| 20045 | Brain Exercises | 121 | 20045 | 03/12/2022 00:00:00 |
| 20001 | SQL Solutions | 156 | 20001 | 07/25/2022 00:00:00 |
| 20045 | Brain Exercises | 255 | 20045 | 07/19/2022 00:00:00 |
| 20001 | SQL Solutions | 125 | 20001 | 07/19/2022 00:00:00 |
| 31111 | Postgres Crash Course | 144 | 31111 | 06/21/2022 00:00:00 |
| 31111 | Postgres Crash Course | 125 | 31111 | 07/04/2022 00:00:00 |
| 32728 | Break the thread | NULL | NULL | NULL |
| 20701 | Tips for Data Analysts | NULL | NULL | NULL |
The way I've thought about solving this is to put the join in a CTE and alias that CTE and then call the column. But I'm not sure that is the right solution. What is the alias of the new table and how can I call the "liked_date" column and check if it's NULL?
This is simple, here you go:
SELECT *
FROM pages p
LEFT JOIN page_likes pl ON p.page_id = pl.page_id
WHERE liked_date IS NULL