Unique constraint on another column if not null - sql

Question

I want to create this table with the following constrains, is it possible to do with SQL Server Management Studio?
Id
ProductId [Nullable column]
CompanyId [Nullable column]
Username [unique for every productId - IF DeletedAt is not NULL]
Identifier [Nullable column] [unique for every companyId - IF DeletedAt is not NULL]
DeletedAt [Nullable column]
Update:
My table create query is the following:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[User](
[Id] [int] IDENTITY(1,1) NOT NULL,
[ProductId] [int] NULL,
[CompanyId] [int] NULL,
[Username] [nvarchar](max) NOT NULL,
[Identifier] [nvarchar](max) NULL,
[DeletedAt] [datetime2](7) NULL,
CONSTRAINT [PK_User] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF,
ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

Answer 1

You'll want to use a unique filtered index. Here you go for the table:
/****** Object: Table [dbo].[the_table] Script Date: 7/26/2018 4:04:00 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[the_table](
[id] [int] NOT NULL,
[productid] [varchar](50) NULL,
[companyid] [varchar](50) NULL,
[username] [varchar](50) NULL,
[identifier] [varchar](50) NULL,
[deleteat] [varchar](50) NULL,
CONSTRAINT [PK_the_table] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
And the index for username:
SET ANSI_PADDING ON
GO
/****** Object: Index [UIDX_USERNAME] Script Date: 7/26/2018 4:03:31 PM ******/
CREATE NONCLUSTERED INDEX [UIDX_USERNAME] ON [dbo].[the_table]
(
[username] ASC
)
WHERE ([DELETEAT] IS NOT NULL)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
It would be the same index logic for the other column, but I don't want to clutter this answer by posting more! I would not mess around with putting the logic in triggers or stored proc's, bad data could still sneak in. If you keep nice constraints, nobody can clutter your data up :)

Answer 2

You can use filtered indexes. The syntax looks like this:
create unique index unq_thetable_username on the_table(username)
where deleteAt is not null;
I don't know if you can point-and-click your way to this solution. I would just write the logic as above.

Answer 3

Create a unique index on ProductId and Username, and use a where clause to restrict that index to WHERE DeletedAt IS NOT NULL. Answer showing an example of a unique filtered index.
You may also need the clause AND ProductId IS NOT NULL, although that wasn't stated as a requirement, but since that column is nullable you ought to think about this.
Similar for Identifier.
You might also want to think about the value of a table where it is valid to have a row where all the columns except Id are null...