Return unique items in SQL query - mysql

Question

SELECT Product.name, Product.price
FROM Purchased, Product
WHERE Purchased.date1 > '2013-11-02'
ORDER BY price DESC group by Product.name
Hello I am writing a query to return a list of unique products that were bought retailer’s site since November the 2nd with most expensive product returned first.
Can anyone tell me what is wrong with my syntax?

Answer 1

You are using MySQL's group by extension incorrectly. Although MySQL allows you to put items in the select list that are not in the group by or an aggregate, it is not deterministic and ORDER BY will not help this.
The MySQL documents state:
The server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate. Furthermore, the selection of values from each group cannot be influenced by adding an ORDER BY clause.
So even if your data was like:
ProductName | Price
------------+----------
A | 2.50
A | 3.50
B | 9.99
Using GROUP BY Product.Name ORDER BY Price DESC is not guaranteed to return the highest price for each product. i.e.
ProductName | Price
------------+----------
A | 3.50
B | 9.99
What you are really saying is "give me one price per product (any price), then order the final results by price". So you could just as easily get 2.50 as the price for product A. I think you could get the results you want by using ``MAX`:
SELECT product.name,
Max(product.price) AS Price
FROM purchased,
product
WHERE purchased.date1 > '2013-11-02'
GROUP BY product.name
ORDER BY price DESC;
I suspect you are also missing a relation between product and purchased, this would be avoided if you used the newer ANSI 92 explicit join syntax, the implicit join syntax you are using is 20 years out of date:
So your final query would be something like:
SELECT product.name,
Max(product.price) AS Price
FROM purchased
INNER JOIN product
ON product.id = purchased.productid
WHERE purchased.date1 > '2013-11-02'
GROUP BY product.name
ORDER BY price DESC;
N.B. I have had to guess at the relationship between Product and Purchased

Answer 2

SELECT
p.name AS Name,
MAX(p.price) AS Price
FROM Purchased AS pr
INNER JOIN Product AS p
ON pr.ProductId=p.ProductId
WHERE pr.date1 > '2013-11-02'
GROUP BY p.name
ORDER BY p.price DESC
I suppose that both your tables, Purchased and Product, have a productId column. This way each record to one table will relate with another record to the other table. If this is not the name of this column, please change the ProductId to the corresponding name.

Answer 3

The first thing you will need to do is find out how the tables are related to one another. I'm going to assume that you have a productid column in your purchased table.
SELECT Product.name, Product.price
FROM Purchased, Product
where Purchased.productid = product.id
and Purchased.date1 > '2013-11-02'
ORDER BY price DESC
What we are doing here is joining the two tables by the id column they have in common. By doing this the database knows what data links together.
Lets say we have the
purchase table
PurchaseDate , Productid,
2013-11-02 1
2013-11-03 2
Product table
id , Product name
1 Fuzzy Bunny
2 Fuzzy bear
Now if you look at that data you know that on 2013-11-02 fuzzy bunny was purchased. You can see this because the productid on your purchase table links back to the id on the product table. That's how you figure out how to work with Joins in SQL.

Answer 4

Referring to your previous question.
SQL Structure help and query
Here is the sqlfiddle
In the query,
group by should be before the order by clause.
SELECT product.name,
product.price
FROM purchased,
product
WHERE purchased.date1 > '2013-11-02'
GROUP BY product.name
ORDER BY price DESC;

Answer 5

Can you please try this:
SELECT Product.name, Product.price
FROM Purchased, Product
WHERE Purchased.date1 > '2013-11-02'
ORDER BY price DESC GROUP BY Product.name,Prodcut.price
When you are using GROUP BY , you must include all the columns that you are retrieving in select class.
Hope this helps.