A better way to aggregate into a default value - sql

Question

For this example I have three tables (individual, business, and ind_to_business). Individual has information on people. Business has information on businesses. And ind_to_business has information on which people are linked to which business. Here are their DDL:
CREATE TABLE individual
(
ID INTEGER PRIMARY KEY,
NAME VARCHAR2(100) NOT NULL,
ENTERPRISE_ID VARCHAR2(25) NOT NULL UNIQUE
);
CREATE TABLE business
(
ID INTEGER PRIMARY KEY,
NAME VARCHAR2(100) NOT NULL,
ENTERPRISE_ID VARCHAR2(25) NOT NULL UNIQUE
);
CREATE TABLE ind_to_business
(
ID INTEGER PRIMARY KEY,
IND_ID REFERENCES individual(id),
BUS_ID REFERENCES business(id),
START_DT DATE NOT NULL,
END_DT DATE
);
I'm looking for the best way to display one row for each person. If they are linked to one business, I want to display the the business's ENTERPRISE_ID. If they are linked to more than one business, I want to display the default value 'Multiple'. They will always be linked to a business, so there is no LEFT JOIN necessary. They can also be linked to a business more than once (Leaving and coming back). Multiple records for the same business would be aggregated.
So for the following sample data:
Individual:
+----+------------+---------------+
| ID | NAME | ENTERPRISE_ID |
+----+------------+---------------+
| 1 | John Smith | 53a23B7 |
| 2 | Jane Doe | 63f2a35 |
+----+------------+---------------+
Business:
+----+----------+---------------+
| ID | NAME | ENTERPRISE_ID |
+----+----------+---------------+
| 3 | ABC Corp | 2a34d9b |
| 4 | XYZ Inc | 34bf21e |
+----+----------+---------------+
ind_to_business
+----+--------+--------+-------------+-------------+
| ID | IND_ID | BUS_ID | START_DT | END_DT |
+----+--------+--------+-------------+-------------+
| 5 | 1 | 3 | 01-JAN-2000 | 31-DEC-2002 |
| 6 | 1 | 3 | 01-JAN-2015 | |
| 7 | 2 | 3 | 01-JAN-2000 | |
| 8 | 2 | 4 | 01-MAR-2006 | 05-JUN-2010 |
| 9 | 2 | 4 | 15-DEC-2019 | |
+----+--------+--------+-------------+-------------+
I would expect the following output:
+---------+------------+------------+
| IND_ID | NAME | LINKED_BUS |
+---------+------------+------------+
| 53a23B7 | John Smith | 2a34d9b |
| 63f2a35 | Jane Doe | Multiple |
+---------+------------+------------+
Here is my current query:
SELECT DISTINCT
sub.ind_id,
sub.name,
DECODE(sub.bus_count, 1, sub.bus_id, 'Multiple') AS LINKED_BUS
FROM (SELECT i.enterprise_id AS IND_ID,
i.name,
b.enterprise_id AS BUS_ID,
COUNT(DISTINCT b.enterprise_id) OVER (PARTITION BY i.id) AS BUS_COUNT
FROM individual i
INNER JOIN ind_to_business i2b ON i.id = i2b.ind_id
INNER JOIN business b ON i2b.bus_id = b.id) sub;
My query works, but this is running on a large dataset and taking a long time to run. I'm wondering if anyone has any ideas on how improve this so that there isn't so much wasted processing (i.e Needing to do a DISTINCT on the final result or doing COUNT(DISTINCT) in the inline view only to use that value in the DECODE above).
I've also created a DBFiddle for this question. (Link)
Thanks in advance for any input.

Answer 1

You could try and use a correlated subquery. This removes the need for outer distinct:
SELECT
i.enterprise_id ind_id,
i.name,
(
SELECT DECODE(COUNT(DISTINCT b.enterprise_id), 1, MIN(bus_id), 'Multiple')
FROM ind_to_business i2b
INNER JOIN business b ON i2b.bus_id = b.id
WHERE i2b.ind_id = i.id
) linked_bus
FROM individual i

Answer 2

You can join with the aggregated ind_to_business per individual. One way to do this:
select i.id, i.name, coalesce(b.enterprise_id, 'Multiple')
from individual i
join
(
select
ind_id,
case when min(bus_id) = max(bus_id) then min(bus_id) else null end as bus_id
from ind_to_business
group by ind_id
) ib on ib.ind_id = i.id
left join business b on b.id = ib.bus_id
order by i.id;

Answer 3

First you should sub-query to get all needed dimensions and then do all your final aggregation using CASE statement.
select
ind_id,
name,
case
when count(*) > 1 then 'Multiple'
else ind_id
end as linked_bus
from
(
select
distinct i.enterprise_id as ind_id,
i.name,
b.enterprise_id as bus_id
from individual i
join ind_to_business i2b
on i.id = i2b.ind_id
join business b
on i2b.bus_id = b.id
) vals
group by
ind_id,
name
order by
ind_id

Answer 4

No need of using DISTINCT twice. You could use subquery factoring and put the in-line view in WITH clause, and make the data set DISTINCT in the subquery itself.
WITH data AS
(
SELECT distinct
i.enterprise_id AS IND_ID,
i.name,
b.enterprise_id AS BUS_ID
FROM individual i
JOIN ind_to_business i2b ON i.id = i2b.ind_id
JOIN business b ON i2b.bus_id = b.id
)
SELECT ind_id,
name,
case
when count(*) = 1 then MIN(bus_id)
else 'Multiple'
end AS LINKED_BUS
FROM data
GROUP BY ind_id, name;
IND_ID NAME LINKED_BUS
---------- ---------- -------------------------
53a23B7 John Smith 2a34d9b
63f2a35 Jane Doe Multiple