how can i do this SQL query in postgreSQL

Question

I am new to the SQL-database, I have tables and columns as follows

productInformation

• productInformationID(primarykey)
• ..
• ..
• price

product

• productId (primary key)
• productInformationID (foreign key)
• ...
• ..

soldProducts

• id(primarykey)
• productID(foreignkey)
• ..

I am trying to find the sold product with the highest quantity and the total price of this sale.

According to this tables, how can I do this query in SQL?

Answer 1

I am assuming every record in your "soldProducts" table is a single quantity. Here you go ( in postgresql ):

1. Grouped by productID to get total quantity in soldProducts, ordered by decreasing quantity and limited to highest sum (1).

2. Select the products having highest total quantity

3. Then, a series of two joins to get to price to calculate total sale.

    SELECT max.productID, max.total_quant , p.price*max.total_quant AS total_sale FROM (SELECT productID, COUNT(*) as total_quant FROM soldProducts GROUP BY productID HAVING COUNT(*) = (SELECT COUNT(*) as total_quant FROM soldProducts GROUP BY productID ORDER BY total_quant DESC LIMIT 1)) as max JOIN products AS p ON max.productID = p.productid JOIN productInformation AS pi ON p.productInformationID = pi.productInformationID ;