I have a table with products and a table with ratings. I have the following query;
SELECT products.name, ratings.rating
FROM products
LEFT OUTER JOIN ratings
ON products.id = ratings.product_id;
Returning me a nice list of rows with the name of the product and every rating separately.
I am trying to achieve that it returns one row showing me the name of the product with its average rating. Can't seem to find out how though.
Thanks in advance.
You want to look into the GROUP BY statement. Example:
SELECT products.name AS Product_Name,
AVG(ratings.rating) AS Average_Rating
FROM products
LEFT OUTER JOIN ratings
ON products.id = ratings.product_id
GROUP BY products.name
ORDER BY products.name;
Whilst using the GROUP BY statement, you may wish to filter your resultset on the outcome of one or more of your aggregate functions. You use the HAVING statement to do so:
SELECT products.name AS Product_Name,
AVG(ratings.rating) AS Average_Rating
FROM products
LEFT OUTER JOIN ratings
ON products.id = ratings.product_id
GROUP BY products.name
HAVING AVG(ratings.rating) >= 3
ORDER BY products.name;
Related
I have two tables products and product_views.
I want to write a query that returns the products with the largest number of views.
products table has id and name columns. product_views has columns id, customer_id, product_id. The counting is based on the product_id column.
Here is my query:
SELECT *
FROM products
LEFT JOIN product_views ON products.id = product_views.product_id
ORDER BY COUNT(product_views.product_id) DESC;
The problem is it returns only the first product. I think the issue is that initially the product_views table is all empty (all values are null).
How to solve this issue?
Based on your criteria, the following should work -
SELECT
p.id,
p.name,
count(v.product_id) as views
FROM products p
LEFT JOIN product_views v
ON p.id = v.product_id
GROUP BY 1,2
ORDER BY views DESC;
The query ignores customer_id, and counts product_ids based on the id/name groupings.
Calculates count in separate script:
SELECT products.id, products.name, pv.count FROM products
JOIN (SELECT product_id, COUNT(*) as count FROM product_views GROUP BY product_id)
pv ON (products.id = product_id )
ORDER BY pv.count DESC;
Example: SQL Fiddle
I have the following tables:
Orders (OID, Count, ProductID, TableNr)
Table (TableNr, Name, Number)
Products (ProductID, Prize)
Now I want to calculate how much was earned per table. I think to do this I have to Group By Orders.TableNr. But how can I multiply the Products.Prize with the Orders.Count and after that sum up this results within the group?
You are describing a join and aggregation:
select o.tableNr, sum(o.count * p.prize) totalEarned
from orders o
inner join products p on p.productId = o.productId
group by o.tableNr
If you want to display table information as well (say, the table name), then you can add another join:
select t.tableNr, t.name, sum(o.count * p.prize) totalEarned
from table t
inner join orders o on o.tableNr = t.tableNr
inner join products p on p.productId = o.productId
group by t.tableNr, t.name
Note that table is a SQL keyword, hence not a good choice for a table name.
I have the tables products and history and I need to group by name:
products = (id_product, name)
history = (id_history, id_product, amount)
I tried this SQL query but it isn't grouped by name:
SELECT
products.name,
sum(history.amount)
FROM history
INNER JOIN products ON history.id_product = products.id_product
GROUP BY
products.name,
history.amount,
history.id_history;
This is the result:
You should only be grouping by the attributes you need to be aggregated. In this case, you need only products.name.
SELECT
products.name,
sum(history.amount) AS [Amount]
FROM history
INNER JOIN products ON history.id_product = products.id_product
GROUP BY
products.name;
If you need to include products without history (assuming sum should be 0 instead of null in this case), then you can use an OUTER JOIN instead of INNER JOIN to include all products:
SELECT
products.name,
COALESCE(sum(history.amount), 0) AS [Amount]
FROM history
RIGHT OUTER JOIN products ON history.id_product = products.id_product
GROUP BY
products.name;
This is no answer, but too long for a comment.
For readability's sake the product table should be first. After all it is products that we select from, plus a history sum that we can access via [left] join history ... followed by an aggregation, or [left] join (<history aggregation query>), or a subselect in the select clause.
Another step to enhance readability is the use of alias names.
Join the table, then aggregate
select p.name, coalesce(sum(h.amount), 0) as total
from products p
left join history h on h.id_product = p.id_product
group by p.name
order by p.name;
Aggregate, then join
select p.name, coalesce(h.sum_amount, 0) as total
from products p
left join
(
select sum(h.amount) as sum_amount
from history
group by id_product
) h on h.id_product = p.id_product
order by p.name;
Get the sum in the select clause
select
name,
(select sum(amount) from history h where h.id_product = p.id_product) as total
from products p
order by p.name;
And as you were confused on how to use GROUP BY, here is an explanation: GROUP BY ___ means you want one result row per ___. In your original query you had GROUP BY products.name, history.amount, history.id_history saying you wanted one result row per name, amount, and id, while you actually wanted one row per name only, i.e. GROUP BY products.name.
I have 2 tables with related data. One table is for products and the other price. In the price table one product may appear several times. How can I return the result by grouping.
Below is my Query but the output is not with Group
SELECT distinct
p.Product,
p.Qty,
MAX(pr.netprice)
FROM Products p
LEFT OUTER JOIN Price pr ON p.Product=pr.Product
WHERE p.brand=''
GROUP BY p.Product, p.Qty
You should probably leave the Qty out of the group by, like this:
SELECT p.Product,
MAX(pr.netprice)
FROM Products p
LEFT OUTER JOIN Price pr ON p.Product=pr.Product
WHERE p.brand=''
GROUP BY p.Product
I have 2 tables with related data.
one table is for products. and the other price. In price table one product may appear several times.
How can I return the result showing the products without containing duplicate rows
My Query is
select p.Product, sum(p.Qty), max(pr.netprice)
from Products p
left outer join Price pr
on p.Product=pr.Product
where p.brand=''
group by p.Product,pr.Product
but return more rows as right table have multiple records
please help
I don't think distinct is the way to go, I think group by should result in what you want if done correctly. Also, I don't think you need to group on values from both tables.. You should really understand what you want to. Give us example data and it will be easier to answer your question. Try this:
select p.Product, sum(p.Qty), max(pr.netprice)
from Products p
left outer join Price pr on p.Product = pr.Product
where p.brand = ''
group by p.Product -- only group on param.
Use the distinct keyword. That will remove duplicates. ALthough, if there are different prices for a given product, there will be one record per unique price per product if you remove the Max().
select DISTINCT p.Product, sum(p.Qty),max(pr.netprice)
from Products p
left outer join Price pr on p.Product=pr.Product
where p.brand='' group by p.Product,pr.Product
Try putting distinct in select. I am not sure it will work, but try it.
If you want the sum then use Tomas answer above. This will give you a unique product list with the total quantity and maximum price for each product
select p.Product, sum(p.Qty), max(pr.netprice)
from Products p
left outer join Price pr on p.Product = pr.Product
where p.brand = ''
group by p.Product
What about changing it this way:
SELECT p.Product, sum(p.Qty),
(SELECT max(pr.netprice)
FROM Price pr
WHERE p.Product=pr.Product
)
FROM Products p
WHERE p.brand=''
Try this
SELECT p.Product, p.Qty, MAX(pr.netprice)
FROM Products p
LEFT OUTER JOIN Price pr ON p.Product=pr.Product
WHERE p.brand=''
GROUP BY p.Product, p.Qty