Prohibit Inserting Rows With Default Constraint - sql

Question

Is there any way of how to prevent inserting data in specified columns in table and use only the default (constraint) values?
E.g. I have columns:
LogInsert (DF GETDATE())
LogUser (DF ORIGINAL_LOGIN())
both defined with DEFAULT constraint. I do not want to allow users to insert into those columns, but use default values here instead when inserting new row.
This should raise an error.
INSERT INTO T1
( C1
,C2
,LogInsert
,LogUser
)
VALUES ( 'A'
,'B'
,'20160101 10:53'
,'domain\user'
);
User should be able to perform the following script without error.
INSERT INTO T1
( C1, C2 )
VALUES ( 'A', 'B' );

Answer 1

You could always give your users a view to work against instead of a table. You can then either choose to hide the columns completely or (as here) make them computed so that they cannot insert a value into the column, via the view:
create table dbo._T1 (
ID int IDENTITY(1,1) not null,
Inserted datetime2 constraint DF__T1_Inserted DEFAULT (SYSDATETIME()) not null,
ABC varchar(10) not null,
constraint PK__T1 PRIMARY KEY (ID)
)
go
create view dbo.T1
with schemabinding
as
select
ID,
COALESCE(Inserted,SYSDATETIME()) as Inserted,
ABC
from dbo._T1
go
insert into dbo.T1 (ABC) values ('abc')
go
insert into dbo.T1 (ABC,Inserted) values ('def',SYSDATETIME())
Results:
(1 row(s) affected)
Msg 4406, Level 16, State 1, Line 19
Update or insert of view or function 'dbo.T1' failed because it contains a derived or constant field.
All of the users queries continue to just use T1. It just happens to be a view rather than a table.
In the above, the view uses COALESCE(Inserted,SYSDATETIME()). It doesn't really matter what's used here, and it doesn't need to match e.g. the default definition. All that's important is that some computation is performed on the Inserted column so that it becomes a read-only column in the view.

Answer 2

You can create a Check Constraint on the table, for example the below
CREATE TABLE [dbo].[T1]
(
[C1] VARCHAR(50)
,[LogInsert] DATETIME DEFAULT GETDATE()
,[LogUser] VARCHAR(500) DEFAULT ORIGINAL_LOGIN()
)
ALTER TABLE [T1] WITH CHECK ADD CONSTRAINT [CK_T1_LogInsert] CHECK ([LogInsert] = GETDATE())
ALTER TABLE [T1] WITH CHECK ADD CONSTRAINT [CK_T1_LogUser] CHECK ([LogUser] = ORIGINAL_LOGIN())
INSERT INTO [dbo].[T1] ([C1]) VALUES ('A')
INSERT INTO [dbo].[T1] ([C1]) VALUES ('B')
INSERT INTO [dbo].[T1] ([C1]) VALUES ('C')
SELECT * FROM [dbo].[T1]
--Will Fail
INSERT INTO [dbo].[T1] ([C1],[LogInsert]) VALUES ('D','2016-11-11 00:00')
INSERT INTO [dbo].[T1] ([C1],[LogUser]) VALUES ('D','Not Your UserName')
OR
You can force the user to only insert using a stored procedure and not allow that as a parameter, this can be done with a table variable too for bulk inserts.