Oracle merge two rows as single row with more columns - sql

Question

I have two tables Employee, Employeerows. I have to pull the employee records who has role 2 or 3.
I have the query below.
SELECT
E.ID,
E.NAME,
ER.PHONE,
ER.ADDRESS,
ER.ROLE
FROM
EMPLOYEE E LEFT JOIN EMPLOYEEROWS ER ON E.ID = ER.ID WHERE ER.ROLE_ID IN (2,3)
This returns either 1 or 2 records for each employee
ID NAME PHONE ADDRESS ROLE
1 ABC 9898989 ABC NJ 2
1 ABC 7878787 ABC XJ 3
2 DEF 7898765 DEF NJ 2
But I have to merge two records into one for that employee with phone number and address as separate columns if the employee has 2 records. My result should like this.
ID NAME PHONE ALT_PHONE ADDRESS ALT_ADDESS
1 ABC 9898989 7878787 ABC NJ ABC XJ
2 DEF 7898765 DEF NJ
Please help me with this.

Answer 1

You can use conditional aggregation. But the left join seems superfluous. You only want to use the left join if you want "employees" that have no rows.
It appears from your data that "2" corresponds to the primary address and "3" to the alternate:
select e.id, e.name,
max(case when er.role_id = 2 then er.phone end) as phone,
max(case when er.role_id = 3 then er.phone end) as alt_phone,
max(case when er.role_id = 2 then er.address end) as address,
max(case when er.role_id = 3 then er.address end) as alt_address
from employee e join
employeerows er
on e.id = er.id
where er.role_id in (2, 3)
group by e.id, e.name;
However, if "2" could be missing, then you would phrase this as:
select e.id, e.name,
max(case when seqnum = 2 then er.phone end) as phone,
max(case when seqnum = 3 then er.phone end) as alt_phone,
max(case when seqnum = 2 then er.address end) as address,
max(case when seqnum = 3 then er.address end) as alt_address
from employee e join
(select er.*,
row_number() over (partition by er.id order by er.role_id) as seqnum
from employeerows er
where er.role_id in (2, 3)
) er
on e.id = er.id
group by e.id, e.name;

Answer 2

You can pivot with conditional aggregation:
select e.id, e.name,
max(case when er.role_id = 2 then er.phone end) as phone,
max(case when er.role_id = 3 then er.phone end) as alt_phone,
max(case when er.role_id = 2 then er.address end) as address,
max(case when er.role_id = 3 then er.address end) as alt_address
from employee e
left join employeerows er on e.id = er.id where er.role_id in (2,3)
group by e.id, e.name

Answer 3

You can use conditional aggregation. But your query is not doing LEFT OUTER JOIN but it is INNER JOIN as you have used the er.role_id in (2,3) in WHERE clause.
Use the following aggreagation technique to fetch the desired result:
SELECT
E.ID,
E.NAME,
MIN(ER.PHONE),
CASE WHEN MIN(ER.PHONE) <> MAX(ER.PHONE) THEN MAX(ER.PHONE) END AS ALT_PHONE,
MIN(ER.ADDRESS),
CASE WHEN MIN(ER.ADDRESS) <> MAX(ER.ADDRESS) THEN MAX(ER.ADDRESS) END AS ALT_ADDRESS
FROM EMPLOYEE E
LEFT JOIN EMPLOYEEROWS ER ON E.ID = ER.ID
AND ER.ROLE_ID IN (2,3) -- added it in the join condition
GROUP BY E.ID, E.NAME;