Question

I am trying to pull invoice data from my database based on a PatientID. I am trying to figure out which invoices belong to which patient. Here is the important parts of my structure.

Invoices Table

InvoiceNumber | DateInvoice | DueDate | StudyID | TypeInvoice 

Patients Table

FirstName | LastName | PatientID

InvoiceFields

id | InvoiceNumber | PatientID | 

I need make a query that lists the invoice table data based upon a PatientID. Below is the query that I attempted, but got no where with. Thank you for your time.

SELECT    Distinct
          invoicefields.InvoiceNumber,
          invoices.DateInvoice
FROM      `invoices`, `patients`, `invoicefields`
WHERE     invoicefields.PatientID = patients.PatientID
          and invoicefields.InvoiceNumber = invoicefields.InvoiceNumber
GROUP BY  invoicefields.InvoiceNumber

Answer 1

SELECT InvT.InvoiceNumber, InvT.DateInvoice
FROM InvoiceTable InvT
INNER JOIN InvoiceFields InvF ON InvF.InvoiceNumber = InvT.InvoiceNumber AND InvF.PatientID = @PatientID

So pretty much since you only need data from the InvoiceTable and you indicate you have the PatientID. I propose you just join to the Cross Reference table InvoiceFields and use the PatientID column in that query to filter it down to what you need. I had a more complex example using an exist before I realized you didn’t need anything from Patients.

You could use this if you need information on the Patient as well (Just put the needed columns in the Select)

SELECT InvT.InvoiceNumber, InvT.DateInvoice
FROM InvoiceTable InvT
INNER JOIN InvoiceFields InvF ON InvF.InvoiceNumber = InvT.InvoiceNumber AND InvF.PatientID = @PatientID
INNER JOIN Patient Pat ON Pat.PatientID = InvF.PatientID

You can put the @PatientID portion on the join for either Patient or InvoiceFields. There really shouldn’t be a performance difference between either way if you indexes are right.

The Response to the Below Comment but where I can show it cleaner:

SELECT  IT.InvoiceNumber
       ,IT.DateInvoice
FROM    InvoiceTable InvT
WHERE   EXISTS (SELECT  InvF.PatientID
                FROM    InvoiceFields InvF
                WHERE   InvF.InvoiceNumber = InvT.InvoiceNumber
                AND InvF.PatientID = @PatientID)

This will return all the rows for the patient from InvoiceTable and if InvoiceNumber is Unique will not have any duplicates. Though this way you only have access to InvoiceTable to return Data from. If you only want one put a TOP 1 on it:

SELECT  TOP 1 IT.InvoiceNumber
       ,IT.DateInvoice
FROM    InvoiceTable InvT
WHERE   EXISTS (SELECT  InvF.PatientID
                FROM    InvoiceFields InvF
                WHERE   InvF.InvoiceNumber = InvT.InvoiceNumber
                AND InvF.PatientID = @PatientID)