I want to find the best customer for each country despite there is one country has two customers the same amount, I want them both to appear.
select customerid,firstname,lastname,country, max(total_amt)
from (select invoice.customerid, customer.firstname,lastname,
sum(invoice.total)total_amt,customer.country
from invoice
join customer
on customer.customerid= invoice.customerid
group by invoice.customerid,customer.country)t2
group by country;
Use window functions:
select c.*
from (select c.country, c.customerid, c.firstname c.lastname, sum(i.total) as total,
dense_rank() over (partition by c.country order by sum(i.total) desc) as seqnum
from customer c join
invoice i
on c.customerid = i.customerid
) c
where seqnum = 1;
Note that I also introduced window functions so the query is easier to write and to read.
Related
I have 2 tables:
CUSTOMERS (ID, FIRSTNAME, LASTNAME, ADDRESS);
ORDERS (ID, PRODUCT_NAME, PRODUCT_PRICE, DATE_ORDER DATE, ID_CUSTOMER, AMOUNT);
Get the first and last names of the customers who bought the biggest amount of a product in one order.
The orders without customer should not be considered. Please sort by FIRSTNAME and LASTNAME
SELECT firstname, lastname
FROM customers
LEFT JOIN orders ON customers.id = orders.id_customer
GROUP BY customers.firstname
HAVING (SELECT MAX(orders.amount) FROM orders);
What I'm doing wrong? thx
If you want one customer with the largest value of amount, then simplest method is order by and then fetching only one row:
select c.firstname, c.lastname
from customers c join
orders o
on c.id = o.id_customer
order by o.amount desc
fetch first 1 row only;
If you want the biggest amount per product, then window functions are the right approach
select pc.*
from (select o.product, c.firstname, c.lastname, o.amount,
rank() over (partition by o.product order by o.amount desc) as seqnum
from customers c join
orders o
on c.id = o.id_customer
) pc
where seqnum = 1;
I’m trying to get from this two tables customer and invoice this information: the total from invoice for every year for each country! So what I wrote is:
SELECT SUM(i.total) AS Total_invoice, strftime(‘%Y’, i.InvoiceDate) AS year, c.country
FROM invoice i JOIN
customer c
ON i.CustomerId = c.CustomerId
GROUP BY 2,3
ORDER BY 1 DESC;
So I get the total of invoice for each year! Now if I want the max(total) for each country how do you do? For example I’d like to have for each country the max( total), the year and the country! Could you help? Tha k you very much enter image description here
For example I’d like to have for each country the max( total), the year and the country!
For this, use window functions:
SELECT yc.*
FROM (SELECT SUM(i.total) AS Total_invoice, strftime(‘%Y’, i.InvoiceDate) AS year, c.country,
ROW_NUMBER() OVER (PARTITION BY c.country ORDER BY SUM(i.total) DESC) as seqnum
FROM invoice i JOIN
customer c
ON i.CustomerId = c.CustomerId
GROUP BY 2, 3
) yc
WHERE seqnum = 1
ORDER BY 1 DESC;
"Write a query that determines the customer that has spent the most on
music for each country. Write a query that returns the country along
with the top customer and how much they spent. For countries where the
top amount spent is shared, provide all customers who spent this
amount.
You should only need to use the Customer and Invoice tables.
Check Your Solution
Though there are only 24 countries, your query should return 25 rows
because the United Kingdom has 2 customers that share the maximum."
You can find the data set here
.
Here is the code I tried with the results
And here is the expected outcome
Generally, you should always GROUP BY anything in your SELECT that is not an aggregation function (e.g. SUM). Try this:
SELECT c.CustomerId, c.FirstName, c.LastName, c.Country,
SUM(i.Total) AS TotalSpent
FROM Customer c
JOIN Invoice i
ON i.CustomerId = c.CustomerId
GROUP BY c.CustomerId, c.FirstName, c.LastName, c.Country
ORDER BY c.Country
WITH tab1 AS ( SELECT c.CustomerId, c.FirstName, c.LastName, c.Country, SUM(i.Total) TotalSpent FROM Customer c JOIN Invoice i ON c.CustomerId = i.CustomerId GROUP BY c.CustomerId ) SELECT tab1.* FROM tab1 left JOIN ( SELECT CustomerId, FirstName, LastName, Country, MAX(TotalSpent) AS TotalSpent FROM tab1 GROUP BY Country ) tab2 ON tab1.Country = tab2.Country WHERE tab1.TotalSpent = tab2.TotalSpent ORDER BY Country;
For example I have to write a query that shows the customer who had spent the most in each country but if a country has two customers with same max value i have to show them both in the output.
I have wrote the query that return the maximum value for each customer in each country but the last country in my example which is 'United Kingdom' has two customers with same maximum values and i couldn't show them both.
SELECT c1.CustomerId, c1.FirstName,c1.LastName,c1.Country,
MAX(c1.TotalSpent) as TotalSpent
FROM
(SELECT c.CustomerId,c.FirstName, c.LastName,i.BillingCountry
Country, SUM(i.Total) totalspent
FROM Customer c
JOIN Invoice i
ON c.CustomerId = i.CustomerId
GROUP BY 1
ORDER BY totalspent
) c1
GROUP BY 4
ORDER BY Country
Use window functions!:
SELECT c.*
FROM (SELECT c.CustomerId, c.FirstName, c.LastName, i.BillingCountry as Country,
SUM(i.Total) as totalspent,
DENSE_RANK() OVER (PARTITION BY i.BillingCountry ORDER BY SUM(i.Total) DESC) as seqnum
FROM Customer c JOIN
Invoice i
ON c.CustomerId = i.CustomerId
GROUP BY c.CustomerId, c.FirstName, c.LastName, i.BillingCountry
) c
WHERE seqnum = 1
ORDER BY Country;
This also fixes your GROUP BY clauses so they are consistent with the columns being selected.
Write a query that determines the customer that has spent the most on music for each country. Write a query that returns the country along with the top customer and how much they spent. For countries where the top amount spent is shared, provide all customers who spent this amount.
You should only need to use the Customer and Invoice tables.
i want to select the customer with the maximum money spent for each country and there is two customers have the same money spent and the same country so when using group by country i got only 1 customer what should i do ?
select c.CustomerId,c.FirstName,c.LastName, c.Country , max(c.Invoices) as TotalSpent
from
(select * , sum(i.Total) as 'Invoices'
from Customer d
join Invoice i on i.CustomerId = d.CustomerId
group by i.CustomerId
) c
group by c.Country
the table i got is the same expected table except 1 customer
Consider joining unit level with two aggregate queries: 1) first to calculate total amount by CustomerId and Country and 2) second to calculate max total amount by Country.
Below assumes your database supports Common Table Expression (CTE) using the WITH clause (nearly supported by all major commercial or open-source RDBMS's). CTE here avoids the need to repeat sum_agg as a subquery.
with sum_agg AS (
select i.CustomerId, sub_c.Country, sum(i.Total) as Sum_Amount
from Customer sub_c
join Invoice i on i.CustomerId = sub_c.CustomerId
group by i.CustomerId, sub_c.Country
)
select c.CustomerId, c.FirstName, c.LastName, c.Country, max_agg.Max_Sum
from Customer c
join sum_agg
on c.CustomerId = sum_agg.Customer_Id and c.Country = sum_agg.Country
join
(select Country, max(Sum_Amount) as Max_Sum
from sum_agg
group by Country
) max_agg
on max_agg.Country = sum_agg.Country and max_agg.Max_Sum = sum_agg.Sum_Amount
Your inner query is almost correct. It should be
select d.*, sum(i.Total) as Invoices
from Customer d
join Invoice i on i.CustomerId = d.CustomerId
group by d.CustomerId
It is allowed to use d.* here, as we can assume d.CustomerId to be the table's primary key, so all columns in the table are functionally dependent on it. If we grouped by d.country instead for instance, that would not be the case and d.* would be forbidden in the select clause (as well as d.firstname etc.). We can only select columns we grouped by (directly or indirectly) and aggregates such as MIN, MAX, SUM etc.
This query gives you the totals per customer along with the customers' countries.
But then you are taking this result and group by country. If you do this, you can only access country and its aggregates. Selecting c.CustomerId for instance is invalid, as there is no the customer ID per country. If your DBMS allows this, it it flawed in this regard and you get a kind of random result.
If your DBMS features window functions, you can get the maximum amounts per country on-the-fly:
select customerid, firstname, lastname, country, invoices
from
(
select
c.*,
sum(i.total) as invoices,
max(sum(i.total)) over (partition by c.country) as max_sum
from customer c
join invoice i on i.customerid = c.customerid
group by c.customerid
) per_customer
where invoices = max_sum
order by country, customerid;
Otherwise you'd have to use your inner query twice, once to get the country totals, once to get the customers matching these totals:
select
c.customerid, c.firstname, c.lastname, c.country,
sum(i.total) as invoices
from customer c
join invoice i on i.customerid = c.customerid
group by c.customerid
having (c.country, invoices) in
(
select country, max(invoices)
from
(
select
--c.customerid, <- optional, it may make this query more readable
c.country,
sum(i.total) as invoices
from customer c
join invoice i on i.customerid = c.customerid
group by c.customerid
) per_customer
);