SQL Server: select records, not linked to another table - sql

Question

I have a table:
CREATE TABLE [dbo].[CollectionSite]
(
[SiteCode] [nvarchar](32) NOT NULL,
[AddressId] [int] NOT NULL,
[RemittanceId] [int] NULL,
// additional columns
)
and a linked table:
CREATE TABLE [dbo].[CollectionSiteAddress]
(
[Id] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](255) NULL,
[Address1] [nvarchar](255) NULL,
[Address2] [nvarchar](255) NULL,
[City] [nvarchar](128) NULL,
[State] [nvarchar](64) NULL,
[Zip] [nvarchar](32) NULL,
)
Relationship between these 2 tables:
ALTER TABLE [dbo].[CollectionSite] WITH CHECK
ADD CONSTRAINT [FK_CollectionSite_CollectionSiteAddress_AddressId]
FOREIGN KEY([AddressId]) REFERENCES [dbo].[CollectionSiteAddress] ([Id])
GO
ALTER TABLE [dbo].[CollectionSite] WITH CHECK
ADD CONSTRAINT [FK_CollectionSite_CollectionSiteAddress_RemittanceId]
FOREIGN KEY([RemittanceId]) REFERENCES [dbo].[CollectionSiteAddress] ([Id])
GO
I want to select all records from CollectionSiteAddress, which are not linked to CollectionSite (neither AddressId nor RemittanceId). Which request should I use?
I tried:
SELECT *
FROM CollectionSiteAddress
LEFT JOIN CollectionSite ON CollectionSiteAddress.Id = CollectionSite.AddressId
OR CollectionSiteAddress.Id = CollectionSite.RemittanceId
but it selects all records from CollectionSiteAddress

Answer 1

You are missing this WHERE clause:
WHERE CollectionSite.[SiteCode] IS NULL
because you want all the unmatched rows of CollectionSiteAddress.
I used the column [SiteCode] to check if it is NULL because it is not nullable in the definition of the table.
So you can write your query like this (shortened with aliases):
SELECT csa.*
FROM CollectionSiteAddress csa LEFT JOIN CollectionSite cs
ON csa.Id = cs.AddressId OR csa.Id = cs.RemittanceId
WHERE cs.[SiteCode] IS NULL
Or use NOT EXISTS:
SELECT csa.*
FROM CollectionSiteAddress csa
WHERE NOT EXISTS (
SELECT 1
FROM CollectionSite cs
WHERE csa.Id = cs.AddressId OR csa.Id = cs.RemittanceId
)