[Dev1462]

After about an hour of trying on my own I've come to seek help, I'm trying to add a check constraint to basically say that if the value of "payment_total = 0" then allow "payment_date" column to be null, while also saying that if "payment_total > 0" to allow payment_date to be not null. Here is the full question for references:

Quote

1. Write an ALTER TABLE statement that adds two new check constraints to the Invoices tables of the AP Schema. The first should allow (1) payment_date to be null only if the payment_total is zero and (2) payment_date to be not null only if payment_total is greater than zero. The second constraint should prevent the sum of payment_total and credit_total from being greater than invoice_total.

ALTER TABLE invoices
ADD CONSTRAINT payment_date_ck 
check ((payment_date is null) and (payment_total = 0));