How to handle multiple rows fulfilling criteria when joining Oracle tables - sql

Question

Given a table of roles, companies and a employee table where we store for each employee which role he/she has at each company.
I'm trying to create a view which indicates for each combination of role and company and employee by a ‘Y’ or ‘N’ in the “checked_yn” column, whether this employee has this role at this company.
company table
----------------
|ID | name |
-----------------
| 1 | A |
| 2 | B |
-----------------
roles table
-------------
|ID | role |
-------------
| 1 | X |
| 2 | Y |
| 3 | Z |
-------------
employee table
----------------------------------------------
|ID | company_id | role_id | employee_log_id |
---------------------------------------------|
| 1 | 1 | 1 | 1 |
| 2 | 1 | 2 | 1 |
| 3 | 2 | null | 1 |
----------------------------------------------
The desired outcome is this:
EMPLOYEE_ROLES_VW view
------------------------------------------------------------------------
|Id |company_id | role_id | Checked_yn | employee_id | employee_log_id |
|----------------------------------------------------------------------|
| 1 | 1 | 1 | Y | 1 | 1 |
| 2 | 1 | 2 | Y | 2 | 1 |
| 3 | 1 | 3 | N | null | 1 |
| 4 | 2 | 1 | N | null | 1 |
| 5 | 2 | 2 | N | null | 1 |
| 6 | 2 | 3 | N | null | 1 |
------------------------------------------------------------------------
This is my current query:
with ROLES_X_COMP as (SELECT ROL.ID AS X_ROLE_ID,
COM.ID AS X_COMPANY_ID,
FROM ROLES ROL
CROSS JOIN COMPANY COM)
SELECT ROWNUM AS ID,
EMP.ID AS SMCR_EMPLOYEE_ID,
EMP.EMPLOYEE_LOG_ID AS EMPLOYEE_LOG_ID,
ROLES_X_COMP.X_ROLE_ID ,
EMP.ROLE_ID AS ROLE_ID,
ROLES_X_COMP.X_COMPANY_ID,
EMP.COMPANY_ID AS COMPANY_ID,
CASE
WHEN ROLES_X_COMP.X_ROLE_ID = SE.ROLE_ID AND ROLES_X_COMP.X_COMPANY_ID =
SE.COMPANY_ID THEN 'Y'
ELSE 'N' END AS CHECKED_YN
FROM ROLES_X_COMP
LEFT OUTER JOIN EMPLOYEE EMP ON ROLES_X_COMP.X_COMPANY_ID = EMP.COMPANY_ID
Because of the join on EMPLOYEE “finds” the company with id=1 twice it joins twice with the cross join of role and company table. So I'm getting this result:
------------------------------------------------------------------------
|Id |company_id | role_id | Checked_yn | employee_id | employee_log_id |
|----------------------------------------------------------------------|
| 1 | 1 | 1 | Y | 1 | 1 |
| 2 | 1 | 2 | N | 1 | 1 |
| 3 | 1 | 3 | N | 1 | 1 |
| 4 | 1 | 1 | N | 2 | 1 |
| 5 | 1 | 2 | Y | 2 | 1 |
| 6 | 1 | 3 | N | 2 | 1 |
| 7 | 2 | 1 | N | 3 | 1 |
| 8 | 2 | 2 | N | 3 | 1 |
| 9 | 2 | 3 | N | 3 | 1 |
------------------------------------------------------------------------
I think a JOIN might be the wrong option here and a UNION more appropriate but I can't figure it out.

Answer 1

Use a partitioned outer join:
Query:
SELECT ROWNUM AS id,
e.company_id,
r.id AS role_id,
NVL2( e.role_id, 'Y', 'N' ) AS CheckedYN,
e.role_id AS employee_id,
e.employee_log_id
FROM roles r
LEFT OUTER JOIN
employee e
PARTITION BY ( e.company_id, e.employee_log_id )
ON ( r.id = e.role_id )
or (depending on how you want to partition and join the data):
SELECT ROWNUM AS id,
c.id AS company_id,
r.id AS role_id,
NVL2( e.role_id, 'Y', 'N' ) AS CheckedYN,
e.role_id AS employee_id,
e.employee_log_id
FROM roles r
CROSS JOIN
company c
LEFT OUTER JOIN
employee e
PARTITION BY ( e.employee_log_id )
ON ( c.id = e.company_id AND r.id = e.role_id )
Output:
Both output the same for the test data but may give differing results depending on your actual data.
ID | COMPANY_ID | ROLE_ID | CHECKEDYN | EMPLOYEE_ID | EMPLOYEE_LOG_ID
-: | ---------: | ------: | :-------- | ----------: | --------------:
1 | 1 | 1 | Y | 1 | 1
2 | 1 | 2 | Y | 2 | 1
3 | 1 | 3 | N | null | 1
4 | 2 | 1 | N | null | 1
5 | 2 | 2 | N | null | 1
6 | 2 | 3 | N | null | 1
db<>fiddle here

Answer 2

AND ROLES_X_COMP.X_ROLE_ID = EMP.ROLE_ID
Is missing at the end of your query
But the outcome will be
EMPLOYEE_ROLES_VW view
------------------------------------------------------------------------
|Id |company_id | role_id | Checked_yn | employee_id | employee_log_id |
|----------------------------------------------------------------------|
| 1 | 1 | 1 | Y | 1 | 1 |
| 2 | 1 | 2 | Y | 2 | 1 |
| 3 | 1 | 3 | N | null | null |
| 4 | 2 | 1 | N | null | null |
| 5 | 2 | 2 | N | null | null |
| 6 | 2 | 3 | N | null | null |
------------------------------------------------------------------------