Create unique constraint initially disabled - tsql

Question

This is my table :
CREATE TABLE [dbo].[TestTable]
(
[Name1] varchar(50) COLLATE French_CI_AS NOT NULL,
[Name2] varchar(255) COLLATE French_CI_AS NULL,
CONSTRAINT [TestTable_uniqueName1] UNIQUE ([Name1]),
CONSTRAINT [TestTable_uniqueName1Name2] UNIQUE ([Name1], [Name2])
)
ALTER TABLE [dbo].[TestTable]
ADD CONSTRAINT [TestTable_uniqueName1]
UNIQUE NONCLUSTERED ([Name1])
ALTER TABLE [dbo].[TestTable]
ADD CONSTRAINT [TestTable_uniqueName1Name2]
UNIQUE NONCLUSTERED ([Name1], [Name2])
GO
ALTER INDEX [TestTable_uniqueName1]
ON [dbo].[TestTable]
DISABLE
GO
My idea is to enable/disable one or other unique contraint depending on the customer application. With this way, I can catch the thrown exception in my c# code, and display a specific error message to the GUI.
Now, my problem is to alter the collation of columns Name1 & Name2, I need to make them case sensitive (French_CS_AS). To alter these fields, I have to drop the two constraints and recreate it. According to the explained schema, I cannot create an enabled constraint and then disable it, because by some customers, I have duplicate keys for one or other constraint.
For my update script, my idea number 1 was
Save the name of enabled constraints in a temp table
Drop the constraints
Alter columns
Create DISABLED unique constraints
Enable specific constraints according to the saved values in points 1.
My problem is in point 4., I don't find how to create a disabled unique constraint with an ALTER TABLE statement. Is it possible to create it directly in the sys.indexes table ?
My idea number 2 was
Rename TestTable to TestTableCopy
Recreate TestTable with the new fields collation, and otherwise the same schema (indexes, FK, triggers, ...)
Disable specifical unique contraints in TestTable
Migrate data from TestTableCopy to TestTable
Drop TestTableCopy
In this way, my fear is to loose some links with other tables/dependencies, beceause it is a central table in my database.
Is there any other way to achieve my goal?
If necessary, I can use unique indexes instead of unique constraints.

Answer 1

It looks like it is impossible to create a unique index on a column that already has duplicate values.
So, rather than having a disabled unique index either:
not have an index at all (which is the same as having a disabled index from the query processor point of view),
or create a non-unique index.
For those instanses where your client has unique data create unique index. For those instanses where your client has non-unique data create non-unique index.

Answer 2

CREATE PROCEDURE [dbo].[spUsers_AddUsers]
#Name1 varchar(50) ,
#Name2 varchar(50) ,
#Unique bit
AS
declare #err int
begin tran
if #Unique = 1 begin
if not exists (SELECT * FROM Users WHERE Name1 = #Name1 and Name2 = #Name2)
begin
INSERT INTO Users (Name1,Name2)
VALUES (#Name1,#Name2)
set #err = ##ERROR
end else
begin
UPDATE Users
set Name1 = #Name1,
Name2 = #Name2
where Name1 = #Name1 and Name2 = #Name2
set #err = ##ERROR
end
end else begin
if not exists ( SELECT * FROM Users WHERE Name1 = #Name1 )
begin
INSERT INTO Users (Name1,Name2)
VALUES (#Name1,#Name2)
set #err = ##ERROR
end else
begin
UPDATE Users
set Name1 = #Name1,
Name2 = #Name2
where Name1 = #Name1
set #err = ##ERROR
end
if #err = 0 commit tran
else rollback tran
So first you check if you need an unique Name1 and Name2 or just Name1. Then if you do you an insert/update based on what constrain you have.