How to make "No Duplicates" column in SQL Server 2008?

Add a unique constraint for that column:

ALTER TABLE Foo ADD CONSTRAINT UQ_Name UNIQUE (Name)

To add it through SQL Management Studio UI:

Open SQL Server Management Studio.
Expand the Tables folder of the database where you wish to create the constraint.
Right-click the table where you wish to add the constraint and click Design.
In Table Designer, click on Indexes/Keys.
Click Add.
Choose Unique Key in the Type drop-down list.

To handle a situation where a unique constraint violation occurs, see for error 2601.

sql-server unique unique-constraint

This can also be done another way with the SSMS GUI if you prefer:

Right click "Indexes" under your table in the SSMS Solution Explorer and click "New Index..." (I know you are looking to create a contstraint, not an index, but this is exactly what the ADD CONSTRAINT SQL script does.

Give new index a name (e.g. "UQ_MyUniqueColumn"), check "Unique", and click "Add..."

sql-server unique unique-constraint

You are looking for the UNIQUE constraint.

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