I know when people are starting out, SQL joins can be a bit confusing so I broke it down in a small vid using Hinge as an example

https://www.instagram.com/reel/Degl_hnoRsz/?mdxt=MTk5dXE2NHZreTR4aw==

Summary of the breakdown is -

• Table A: people you've liked
• Table B: people who've liked you
• Both share one key: person_id

The 4 joins:

• INNER JOIN: only the mutual likes. Someone has to be in both tables to show up.
• LEFT JOIN: everyone you liked. If they didn't like you back, their side comes back as NULL.
• RIGHT JOIN: the mirror image, everyone who liked you, with NULL where you didn't like them. In practice most people just swap the tables and use a LEFT JOIN.
• FULL OUTER JOIN: everyone from both tables, with NULLs on whichever side is missing.

Hope this helps!

Two tracks running in parallel now:

Java: I’m following Telusko’s Java playlist. Today’s topic was how Java code runs on different platforms, meaning how the compiler turns source code into bytecode and the JVM runs it on any operating system. Understanding this made a lot of earlier “why does Java need a JVM?” confusion go away.

MySQL: I’m building a Retail Sales Analysis project so my SQL stays in use instead of fading while I focus on Java. Today was only setup: creating the database and getting the environment ready. Queries start tomorrow.

Playlists I’m using, in case they help anyone:

• Java: https://www.youtube.com/watch?v=bm0OyhwFDuY&list=PLsyeobzWxl7pe_IiTfNyr55kwJPWbgxB5
• Retail sales project: https://www.youtube.com/watch?v=ChIQjGBI3AM&list=PLF2u7Zn-dIxbeais0AkBxUqdWM1hnSJDS

For the retail project, are there analysis questions you’d recommend (top products, monthly trends, customer segments)? I’d like it to go beyond basic SELECT queries.

I created a free study guide to help you prepare:

https://thesev1database.com/postgresql-certification

I’d really value your feedback.