how to get the difference between 2 tables in 2 different schema's in Oracle?
To mustaccio's point, there's nothing particular about a schema that prevents you from querying objects from different schemas within the same query (putting privileges aside - since that's a function of security, not a unique feature of schemas).
So you can use a FULL JOIN between the two tables across schemas with an appropriate WHERE clause like so to answer your questions:
-- Gets all rows that have the same primary key (ticket_number) between the two tables
SELECT * -- Replace * with only the columns you need, as using * is generally bad practice
FROM tickets1.Tickets T1
FULL JOIN tickets2.Tickets T2
    ON T1.ticket_number = t2.ticket_number
WHERE T1.ticket_number IS NOT NULL
    AND T2.ticket_number IS NOT NULL

-- Gets all rows that have different primary keys (ticket_number) between the two tables
SELECT * -- Replace * with only the columns you need, as using * is generally bad practice
FROM tickets1.Tickets T1
FULL JOIN tickets2.Tickets T2
    ON T1.ticket_number = t2.ticket_number
WHERE (T1.ticket_number IS NOT NULL AND T2.ticket_number IS NULL)
    OR  (T1.ticket_number IS NULL AND T2.ticket_number IS NOT NULL)

Note the above only compares the two tables by the primary key (ticket_number). Depending on your definition of &quot;same data&quot; / &quot;different data&quot;, you may want to compare by other fields in the tables as well.