take a look at https://bobj-board.org/t/100493 this seems to be the same question.
Doing an inner join where table1.field1 <> table2.field2 is very different to outer join table1.field1 = table2.field2. This first is matching table1 with every record in table2 that does not have a matching field2 value, whereas the second is only finding a match if there is a matching field2 value…and you’d add a second query to then filter out the ones where table2.field2 is null (it did not find a match)
HuwD 
(BOB member since 2007-04-19)