Postgres join and count multiple relational tables - sql

Question

I want to join the 2 tables to the first table and group by a vendor name. I have three tables listed below.
Vendors Table
| id | name
|:-----------|------------:|
| test-id | Vendor Name |
VendorOrders Table
| id | VendorId | Details | isActive(Boolean)| price |
|:-----------|------------:|:------------:| -----------------| --------
| random-id | test-id | Sample test | TRUE | 5000
OrdersIssues Table
| id | VendorOrderId| Details. |
|:-----------|--------------:-----------:|
| order-id | random-id | Sample test|
The expected output is to count how many orders belong to a vendor and how many issues belongs to a vendor order.
I have the below code but it's not giving the right output.
SELECT "vendors"."name" as "vendorName",
COUNT("vendorOrders".id) as allOrders,
COUNT("orderIssues".id) as allIssues
FROM "vendors"
LEFT OUTER JOIN "vendorOrders" ON "vendors".id = "vendorOrders"."vendorId"
LEFT OUTER JOIN "orderIssues" ON "orderIssues"."vendorOrderId" = "vendorOrders"."id"
GROUP BY "vendors".id;```

Answer 1

You need the keyword DISTINCT, at least for allOrders:
SELECT v.name vendorName,
COUNT(DISTINCT vo.id) allOrders,
COUNT(DISTINCT oi.id) allIssues
FROM vendors v
LEFT OUTER JOIN vendorOrders vo ON v.id = vo.vendorId
LEFT OUTER JOIN orderIssues oi ON oi.vendorOrderId = vo.id
GROUP BY v.id, v.name;
Consider using aliases instead of full table names to make the code shorter and more readable.

Answer 2

You are joining along two related dimensions. The overall number of rows is the number of issues. But to get the number of orders, you need a distinct count:
SELECT v.*, count(distinct vo.id) as num_orders,
COUNT(oi.vendororderid) as num_issues
FROM vendors v LEFT JOIN
vendorOrders vo
ON v.id = vo.vendorId LEFT JOIN
orderIssues oi
ON oi.vendorOrderId = vo.id
GROUP BY v.id;
Notes:
Table aliases make the query easier to write and to read.
Quoting column and table names makes the query harder to write and read. Don't quote identifiers (you may need to recreate the tables).
Postgres support SELECT v.* . . . GROUP BY v.id assuming that the id is the primary key (actually, it only needs to be unique). This seems like a reasonable assumption.