subquery error in group by when converting from MySQL to PostgresSQL - mysql

Question

I'm converting my database from MySQL to PostgresSQL, and I have this query which tries to sord the products by the cheapest price and the most popular in a given location. It works fine in MySQL, but in Postgres I'm running into problems with this query :
SELECT products.product_id,
suppliers.supplier_id,
product_code.desc_fa,
products.name_fa,
MIN(product_supplier.price) AS price,
SUM(COALESCE(orders.quantity, 0)) AS n_orders
FROM products
JOIN product_code ON product_code.code_id = products.code_id
JOIN product_supplier ON product_supplier.product_id = products.product_id
JOIN suppliers ON suppliers.supplier_id = product_supplier.supplier_id
JOIN product_tags ON product_tags.product_id = products.product_id
JOIN tags ON tags.tag_id = product_tags.tag_id
JOIN product_crop ON product_crop.product_id = products.product_id
JOIN crops ON crops.crops_id = product_crop.crop_id
LEFT JOIN orders
ON orders.product_id = products.product_id and orders.crop_id = product_crop.crop_id
LEFT JOIN user ON user.user_id = orders.user_id and user.location_id = 883
WHERE crops.crops_id = 1
AND product_supplier.quantity >= 3
AND tags.tag = 'علف کش'
GROUP BY products.name_fa
ORDER BY n_orders DESC
LIMIT 10;
It gives me this error :
column must appear in the GROUP BY clause or be used in an aggregate function
Any suggestions to how to work around this error ?
UPDATE :
According to the answers i was able to make it work by using this query:
WITH tem_1 AS (SELECT product_id, MIN(price) AS price FROM product_supplier GROUP BY product_id) ,
tem_2 AS (SELECT product_id, SUM(quantity) AS n_orders FROM orders Group by product_id)
SELECT products.product_id, suppliers.supplier_id, product_code.desc_fa, products.name_fa, tem_1.price,
products.telegraph, suppliers.location_id, COALESCE(tem_2.n_orders,0) AS quant FROM products
INNER JOIN product_supplier ON product_supplier.product_id = products.product_id
INNER JOIN suppliers ON suppliers.supplier_id = product_supplier.supplier_id
INNER JOIN product_code ON product_code.code_id = products.code_id
INNER JOIN product_crop ON product_crop.product_id = products.product_id
INNER JOIN crops ON crops.crops_id = product_crop.crop_id
INNER JOIN product_tags ON product_tags.product_id = products.product_id
INNER JOIN tags ON tags.tag_id = product_tags.tag_id
INNER JOIN tem_1 ON tem_1.price = product_supplier.price AND tem_1.product_id = products.product_id
LEFT JOIN tem_2 ON tem_2.product_id = products.product_id
WHERE crops.crops_id = 1 AND product_supplier.quantity >= 3 AND tags.tag = 'علف کش'
ORDER BY quant DESC
LIMIT 10;;
But since i'm fairly new to SQL, I wanted to know if my code is correct or is there a better way to implement it?

Answer 1

When you use aggregate function (as SUM, MIN and others) the other columns in your field list without aggregate function must be included in GROUP BY clause.
These fields:
products.product_id,
suppliers.supplier_id,
product_code.desc_fa,
products.name_fa
must be in GROUP BY.
Instead your GROUP BY clause has only the following field:
products.name_fa
You must add the other missing 3 fields
In MySql this error has turned off by default, so your query works fine, but in other DBMS you are in an error case.
You can see here how set MySql environment about the GROUP BY behaviour