In MySQL, if you have two tables with a shared index and you would like to show the results of one table where the index is not within another table, you can use “NOT IN”.
SELECT * FROM table2 WHERE some_field not in
(SELECT some_field FROM table1)
Try Googling “MySQL NOT IN” and you get everything but this command, it’s almost as if they need to have an alias for this simple command since these two words are in EVERYTHING and on so many web pages. Perhaps “NOTCONTAINEDIN” would be better, all in one word? Just a suggestion.
In the sub-select, the query inside parenthesis, you can take this a step further and apply conditions to the filter so you can exclude results in “table2” more narrowly than just being in “table1”, perhaps if “table1” had a status of “EXPIRED” in a field, then you could add that criteria to be more selective.