Cascade error (1 Viewer)

[Winterwolf73]

Ok all, I have no idea what I did. But I got the relationships set up. However, now when I add the customer number, I get the following error.

Cannot perform cascading operation. It would result in a duplicate key in table.

I have attached a copy of the DB for reference.

 

[plog]

Your 1-many relationships are incorrect and you are not using your primary keys correctly.

When you make a 1-many relationship between tables (e.g. tblCustInfo / tblProjects) the primary key value of the 1 table (tblCustInfo) goes into the many table (tblProjects). So, Project_ID needs to come out of tblCustInfo and a field to hold the ID value of tblCustInfo should be made in tblProjects.

Here's a good link explaining primary/foreign keys:

SQL FOREIGN KEY Constraint

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Additionaly, you shouldn't have a 1-1 relationship, instead you simply put all the data into 1 table. You have a 1-1 between tblCustInfo and tblInvoices--if its true a customer can have just 1 invoice, then put all those fields in 1 table. But it doesn't seem correct--can't a customer have multiple invoices?

Lastly, no spaces or special characters in names, it just makes coding/querying that more difficult. Only use alphanumeric characters and underscores ([Type Of Payment] - TypeOfPayment)

 

[Winterwolf73]

So it would be better if I went from tblCustInfo to tblInvoices(1 - Many) as each customer could have multiple invoices. I could eliminate tblProjects as this would be covered by the invoices table.

 

[plog]

Possibly. I don't fully understand how your organization operates. Answer these---

1. Will there be only 1 invoice per project?
2. Could one invoice contain data from multiple projects?

At a quick glance those can seem like the exact same question but the are different.

 

[Winterwolf73]

To answer your questions,
1. There will only be one invoice per project.
2. it all depend. But, more than likely not.

 

[plog]

If an invoice can contain data from multiple projects you will need an invoice table