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How do I specify a SQL Server constraint to ensure one column is NOT NULL if another column has a certain value?

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Last Modified: 2015-04-27
Suppose we have a table:

CREATE TABLE Invoice
 (InvoiceId int...,
  RequiresDelivery bit NOT NULL,
  DeliveryAddressId int NULL CONSTRAINT FK_Invoice_Address_Delivery REFERENCES Address(AddressId)
)

If the column RequiresDelivery is set to 1 then the DeliveryAddressId needs to have a value, but if RequiresDelivery is set to 0, it is ok for DeliveryAddressId to be NULL.

How do I express this as a SQL constraint - or do I have to use a trigger?

This is for SQL Server 2012 and later.
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