I have 3 different tables :
Client
+----+-----------+----------+
| id | firstName | lastName |
+----+-----------+----------+
| 1 | John | Doe |
| 2 | Jane | Doe |
+----+-----------+----------+
Loan
+----+--------+-----------+----------------+
| id | amount | client_id | institution_id |
+----+--------+-----------+----------------+
| 1 | 200 | 2 | 3 |
| 2 | 400 | 1 | 1 |
+----+--------+-----------+----------------+
Institution
+----+---------------+
| id | name |
+----+---------------+
| 1 | Institution A |
| 2 | Institution B |
| 3 | Institution C |
+----+---------------+
I am looking to create a list of the number of loans a client has with each institution (for every row in the institution table). Including when a client has 0 loans with an institution.
Something that looks like :
+-----------+-----------+----------+--------------------------+-----------+
| client_id | firstName | lastName | financialInstitutionName | loanCount |
+-----------+-----------+----------+--------------------------+-----------+
| 1 | John | Doe | Institution A | 1 |
| 1 | John | Doe | Institution B | 0 |
| 1 | John | Doe | Institution C | 0 |
| 2 | Jane | Doe | Institution A | 0 |
| 2 | Jane | Doe | Institution B | 0 |
| 2 | Jane | Doe | Institution C | 1 |
+-----------+-----------+----------+--------------------------+-----------+
I have tried all manners of joins, subqueries and where clauses but without success. The concept that I do not grasp is how to get a row per institution, per client (total count institution x client). I would love if that query was possible without subqueries or union joins.
Thank you for your time!
SELECT
loan.client_id,
client.firstName,
client.lastName,
institution.name as financialInstitutionName,
COUNT(loan.id) as loanCount
FROM client
INNER JOIN loan ON client.id = loan.client_id
INNER JOIN institution ON loan.institution_id = institution.id
GROUP BY client.id;
First subquery in the FROM
setups that data so each client has a record for each of the institutions. This is then joined to a subquery that counts the number of loans.
SELECT
d.client_id,
d.firstName,
d.lastName,
d.name AS financialInstitutionName,
CASE WHEN l IS NULL
THEN 0
ELSE l.loanCount
END AS loanCount
FROM
(
SELECT
Client.id AS client_id,
Client.firstName,
Client.lastName,
Institution.id AS institution_id,
Institution.name
FROM Client, Institution
) AS d
LEFT JOIN (
SELECT client_id, institution_id, COUNT(id) AS loanCount
FROM Loan
GROUP BY client_id, institution_id
) AS l ON d.client_id = l.client_id AND d.institution_id = l.institution_id
Edit: Includes a record for each institution
Edit: Spelling
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