Please help with some query

Question

hello all!
please, help me again.
we have a foreign key discrepancy and my task is to create a view which will show the 3 aspects.
Let's we have 3 schemas: A - good (which means that i will compare WITH A, source)
B and C are bad (which mean that I will checking this schemas).
So, i need to obtain:
1) FK that DO NOT exist in B&C and do exist in A
2) FK that DO exist in bad schemas (B&C) but DO NOT exist in good schema (A)
3) FK's that exist in both (A&B, A&C) schemas on the SAME TABLE, have THE SAME CONSTRAINT_NAME but are on the DIFFERENT columns.
the first and second I seem to be done through the
select CONSTRAINT_NAME, TABLE_NAME, STATUS from dba_constraints where owner='PRIV_MD' and CONSTRAINT_TYPE='R' and CONSTRAINT_NAME
2 NOT IN (select CONSTRAINT_NAME from dba_constraints where owner ='MSA_MD'); (to get the second task we just reversing owners in query and subquery)
query. but the third one is really pain in my back. i have a query:
SELECT a.column_name, b.column_name FROM dba_cons_columns a, dba_cons_columns b, dba_constraints c, dba_constraints d
WHERE c.CONSTRAINT_TYPE='R'
AND a.CONSTRAINT_NAME = b.CONSTRAINT_NAME
AND a.CONSTRAINT_NAME = c.CONSTRAINT_NAME
AND b.CONSTRAINT_NAME = d.CONSTRAINT_NAME
AND a.owner = 'PRIV_MD' AND b.owner = 'MSA_MD';
which runs hours and returns million of rows with the two columns with the same names... but if i'm adding
AND a.column_name != a.column_name (i'm not sure it's a correct syntax)
line it returns "no rows selected"
please, help me obtain it, i'm fighting already the second day..
(please, don't be angry, i'm just learning and this is my first task on my work...)

Answer 1

This is basically just a UNION ALL (the constraint columns from both schemas)
MINUS what exists in both (the INTERSECTion)
I made it a little more complicated so you could see in which schema the column is used. You could use exactly the same approach for your questions 1 and 2 also.
SELECT * FROM
(SELECT a.column_name,c.constraint_name,'salive' schema_containing
FROM dba_cons_columns a
INNER JOIN dba_constraints c ON a.CONSTRAINT_NAME = c.CONSTRAINT_NAME
WHERE a.owner = 'SALIVE' and c.constraint_type = 'R'
UNION ALL
select b.column_name,d.constraint_name,'satest'
FROM dba_cons_columns b
INNER JOIN dba_constraints d ON b.CONSTRAINT_NAME = d.CONSTRAINT_NAME
WHERE d.CONSTRAINT_TYPE='R' AND b.owner = 'SATEST') u
WHERE NOT EXISTS
(SELECT *
FROM
(SELECT a.column_name,c.constraint_name
FROM dba_cons_columns a
INNER JOIN dba_constraints c ON a.CONSTRAINT_NAME = c.CONSTRAINT_NAME
WHERE a.owner = 'SALIVE' and c.constraint_type = 'R'
INTERSECT
select b.column_name,d.constraint_name
FROM dba_cons_columns b
INNER JOIN dba_constraints d ON b.CONSTRAINT_NAME = d.CONSTRAINT_NAME
WHERE d.CONSTRAINT_TYPE='R' AND b.owner = 'SATEST') i
WHERE u.column_name = i.column_name and u.constraint_name = i.constraint_name)