MySQL JOIN with multiple tables and SUMS - mysql

Question

I am trying to create a query that will take information out of four tables for a billing system that I am creating. I have the following tables:
Table Invoice
InvoiceID (PK)
ClientID
Date
Status
...
Table Client
ClientID (PK)
ClientName
...
Table InvoiceItem
ItemID (PK)
InvoiceID
Amount
...
Table Payments
PaymentID (PK)
InvoiceID
Amount
...
I need to create a query where I can access information from the Invoice table along with the client name, and the sum of all invoice items and payments associated with the invoice.
I have tried the following:
SELECT
Invoice.InvoiceID,
Invoice.`Date`,
Invoice.Terms,
Invoice.DateDue,
Invoice.Status,
Client.ClinicName,
SUM(InvoiceItem.Amount),
SUM(Payment.PaymentAmount)
FROM Invoice
JOIN (Client, InvoiceItem, Payment) ON
(Client.ClientID=Invoice.ClientID AND
InvoiceItem.InvoiceID=Invoice.InvoiceID AND
Payment.InvoiceID=Invoice.InvoiceID)
And while this kind-of works, it is multiplying the SUM() by the number of records used to get the sum (i.e. if there are two payments - 800,400 - It gives me (800+400)*2 -- 2400). I am guessing that there is something with how I am using the join, and I have honestly never had to use join for more than one table, and I would always use GROUP BY, but I can't seem to get that to work correctly.
To make matters worse, I have been lost to the world of vb.net/MSSQL client-side programming for the past several years, so my MySQL is rather rough.

Answer 1

Your problem is that you can't aggregate over two independent tables at once in a single query. However you can do it using subqueries.
SELECT Invoice.InvoiceID, Invoice.`Date`, Invoice.Terms, Invoice.DateDue, Invoice.Status, Client.ClinicName, InvoiceItemSum.SumOfAmount, PaymentSum.SumOfPaymentAmount
FROM Invoice
INNER JOIN Client ON Client.ClientID = Invoice.ClientID
INNER JOIN (
SELECT InvoiceID, SUM(Amount) AS SumOfAmount
FROM InvoiceItem
GROUP BY InvoiceID
) InvoiceItemSum ON InvoiceItemSum.InvoiceID = Invoice.InvoiceID
INNER JOIN (
SELECT InvoiceID, SUM(PaymentAmount) AS SumOfPaymentAmount
FROM Payment
GROUP BY InvoiceID
) PaymentSum ON PaymentSum.InvoiceID = Invoice.InvoiceID

Answer 2

Here try this one
SELECT a.InvoiceID,
a.`Date`,
a.Terms,
a.DateDue,
a.Status,
b.ClinicName,
SUM(c.Amount),
SUM(d.PaymentAmount)
FROM Invoice a
INNER JOIN Client b
on a.ClientID = b.ClientID
INNER JOIN InvoiceItem c
ON c.InvoiceID = a.InvoiceID
INNER JOIN JOIN Payment d
ON d.InvoiceID = a.InvoiceID
GROUP BY a.InvoiceID,
a.`Date`,
a.Terms,
a.DateDue,
a.Status,
b.ClinicName
can you elaborate more on this?
it is multiplying the SUM() by the number of records used to get the
sum (i.e. if there are two payments - 800,400 - It gives me
(800+400)*2 -- 2400)

Answer 3

Try this:
SELECT
Invoice.InvoiceID,
Invoice.`Date`,
Invoice.Terms,
Invoice.DateDue,
Invoice.Status,
Client.ClinicName,
SUM(InvoiceItem.Amount),
SUM(Payment.PaymentAmount)
FROM Invoice
JOIN Client ON Client.ClientID=Invoice.ClientID
JOIN InvoiceItem ON InvoiceItem.InvoiceID=Invoice.InvoiceID
JOIN Payment ON Payment.InvoiceID=Invoice.InvoiceID
group by 1,2,3,4,5,6;
I did two things to your query:
Created separated joins for each of the child tables
Added a group by, without which the sum won't work correctly (fyi, in all other databases, omitting the group by would actually result in a syntax error)

Answer 4

you can also achive it by "CROSS APPLY"
SELECT Invoice.InvoiceID, Invoice.`Date`, Invoice.Terms, Invoice.DateDue, Invoice.Status, Client.ClinicName, InvoiceItemSum.SumOfAmount, PaymentSum.SumOfPaymentAmount
FROM Invoice
INNER JOIN Client ON Client.ClientID = Invoice.ClientID
CROSS APPLY ( SELECT ISNULL(SUM(Amount),0) AS SumOfAmount
FROM InvoiceItem
WHERE InvoiceID = Invoice.InvoiceID
) InvoiceItemSum
CROSS APPLY ( SELECT ISNULL(SUM(PaymentAmount),0) AS SumOfPaymentAmount
FROM Payment
WHERE InvoiceID = Invoice.InvoiceID
) PaymentSum