Finding records in TableA that don't exist in Table B in MySql

Question

I have a multi-million Table A which includes Field1

I have another similar Table B

I have done various queries prior on Table A/Field 1

I'd like to try to isolate those Field1s in TableB I am going to need to run similar queries on

So I'd like to basically extract a list of Field1 from TableB where that Field1 does NOT already exist in TableA so I can start to process those records.

Answer 1

I think the fastest way would be:

SELECT b.*, a.id 
FROM b
LEFT JOIN a
ON b.field1 = a.field1
WHERE a.id IS NULL;

Answer 2

select field1 
from tableB 
where not exists (select * from tableA where tableB.field1 = tableA.field1)