MySQL snippet - Selecting from table a items that aren't in table b

How I found items that were present in one table but not another

Today I needed to select something from a table on the condition that the ID of the row in the table did not appear in another table.

Initially I thought this was going to be slightly difficult to do, or at least a bit convoluted but it turned out to be really simple.

SELECT FROM table_a LEFT JOIN table_b ON = table_b.aid WHERE table_b.aid IS NULL;

Since you are using a LEFT JOIN table_b.aid can return NULL values, and these are the ones you are looking for.

Recent posts View all

Web Dev

Creating Docker images with M1 Macs

I ran into an issue with my Dockerfile when using it on a Linux machine, setting a platform fixed the issue

Web Dev

What does --no-owner mean in Postgres?

You have read a guide to doing Postgres exports or imports and seen --no-owner, this is what it means