můžete použít mínus
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( extract(month from sysdate), 2,'0')
minus
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( (extract(month from sysdate) -1) , 2,'0')
a pokud potřebujete obsah řádků
select * from my_table m
inner join (
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( extract(month from sysdate), 2,'0')
minus
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( (extract(month from sysdate) -1) , 2,'0')
) T on m.SYS_DB_NAME = t.SYS_DB_NAME
AND m.ENTITY_ID = t.ENTITY_ID
AND m.MONTH_ID = t.MONTH_ID
a pokud potřebujete pouze počítat
select count(*) from
inner join (
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( extract(month from sysdate), 2,'0')
minus
select SYS_DB_NAME, ENTITY_ID, MONTH_ID
from my_table
where MONTH_ID = to_char(sysdate, 'YYYY') || lpad( (extract(month from sysdate) -1) , 2,'0')
) T