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

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 table_a.id FROM table_a LEFT JOIN table_b ON table_a.id = 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

TextExpander

TextExpander Usage Statistics

I was curious about how TextExpander calculated usage across different apps, here is what I've found

Rails

Making your Trix toolbar sticky

Editing long sections of text can be cumbersome with the Trix editor. Let's make it better.