Since your send query only returns a single field (possibly with many values?), look into subquery
] formulated much like below:
SELECT * FROM Table1 WHERE field1 NOT IN (SELECT field2 FROM table 2)
There are variations on this and, under appropriate conditions (only return a single value from a single field) they can be in your SELECT as well.
Leaning more SQL and it gets easier to write: Certain tasks were so useful they were made into language features.