How to fetch the non matching rows in Oracle - sql

Question

Can anyone help me fetch the non matching rows from two tables in Oracle?
Table: Names
Class_id Stud_name
S001 JAMES
S001 PETER
S002 MARK
Table: Course
Course_id Stud_name
S001 JAMES
S001 KEITH
S002 MARK
Output
I need the rows to display as
CLASS ID STUD_NAME_FROM_NAME_TABLE STUD_NAME_FROM_COURSE_TABLE
---------------------------------------------------------------------
S001 PETER KEITH
I have used Oracle joins to fetch the non matching names:
SELECT *
FROM Names, Course
WHERE Names.Class_id=Course.Course_id
AND Names.Stud_name<>Course.Stud_name
This query is returning duplicate rows.

Answer 1

If you insist on Join you can use this one:
SELECT *
FROM Names
FULL OUTER JOIN Course ON Names.Class_id=Course.Course_id
AND Names.Stud_name = Course.Stud_name
WHERE Names.Stud_name IS NULL or Course.Stud_name IS NULL

Answer 2

Fetches unmatched rows in Names table
SELECT * FROM Names
WHERE
NOT EXISTS
(SELECT 'x' from Course
WHERE
Names.Class_id = Course.Course_id AND
Names.Stud_name = Course.Stud_name)
Fetches unmatched rows in Names and Course too!
SELECT Names.Class_id,Names.Stud_name,C1.Stud_name
FROM Names , Course C1
WHERE Names.Class_id = C1.Course_id AND
NOT EXISTS
(SELECT 'x' from Course C2
WHERE
Names.Class_id = C2.Course_id AND
Names.Stud_name = C2.Stud_name);

Answer 3

When you ask for unmatching rows I assume that you want rows that exist in names but not in course.
If this is the case you're probably after
select * from names
where (class_id, stud_name ) not in
(select course_id, stud_name from course);
Your query returned duplicate rows beacuse for each row in names it selected all rows in course that satisfied the where condition.
So, for the row S001, PETER in names it faound that S001, JAMES and S001, KEITH matched that condition, thus, that row was "returned" twice.
EDIT Since it is not clear if stud_name is a primary key, or unique (and on second sight I think it's not), you'd probably want a
select * from names
where not exists (
select 1 from course where
names.class_id = course.course_id and
names.stud_name <> course.stud_name
)
Edit II if you insist on using a join (as per your comment) you might want to try a
select distinct names.* from...

Answer 4

Hope it helps you
with not_in_class as
(select a.*
from Names a
where not exists ( select 'x'
from course b
where b.Course_id = a.class_id
and a.Stud_name = b.Stud_name)),
not_in_course as
(select b.*
from course b
where not exists ( select 'x'
from Names a
where b.Course_id = a.class_id
and a.Stud_name = b.Stud_name))
select x.class_id,
x.Stud_name NOT_IN_CLASS,
y.stud_name NOT_IN_COURSE
from not_in_class x, not_in_course y
where x.class_id = y.course_id
Output
| CLASS_ID | NOT_IN_CLASS | NOT_IN_COURSE |
|----------|--------------|---------------|
| S001 | PETER | KEITH |
Only problem is that if multiple mismatches are there in both the tables for a given id, it works for single mismatch for a particular id. You need to rework if multiple mismatches are there for the same id.

Answer 5

Well, I am not sure if I understand correctly what you are asking. I think you want a list of all IDs where the student list in class table and course table differs. Then you want to show the id and the students that are in class but not in course and the students that are in course but not in class.
To do so you would full outer join the tables. That gives you students that are both in class and course, students that are in class and not in course, and students that are in course and not in class. Filter your results where either class_id or course_id is null then to get the students missing in course or class. At last group by id and list the students.
select coalesce(class.class_id, course.course_id) as id
, listagg(class.stud_name, ',') within group (order by class.stud_name) as missing_in_course
, listagg(course.stud_name, ',') within group (order by course.stud_name) as missing_in_class
from class
full outer join course
on (class.class_id = course.course_id and class.stud_name = course.stud_name)
where class.class_id is null or course.course_id is null
group by coalesce(class.class_id, course.course_id);
Here is the SQL fiddle showing how it works: http://sqlfiddle.com/#!4/8aaaa/2
EDIT: In Oracle 9i there is no listagg. You can use the inofficial function wm_concat instead:
select coalesce(class.class_id, course.course_id) as id
, wm_concat(class.stud_name) as missing_in_course
, wm_concat(course.stud_name) as missing_in_class
from class
full outer join course
on (class.class_id = course.course_id and class.stud_name = course.stud_name)
where class.class_id is null or course.course_id is null
group by coalesce(class.class_id, course.course_id);