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modify-unique-constraints.md

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title Modify Unique Constraints
description Learn how to modify Unique Constraints in SQL Server Management Studio (SSMS) or T-SQL.
author WilliamDAssafMSFT
ms.author wiassaf
ms.date 08/07/2025
ms.service sql
ms.subservice table-view-index
ms.topic how-to
ms.custom
ignite-2025
helpviewer_keywords
modifying constraints
UNIQUE constraints [SQL Server], modifying
constraints [SQL Server], modifying
constraints [SQL Server], unique
monikerRange =azuresqldb-current || >=sql-server-2016 || >=sql-server-linux-2017 || =azuresqldb-mi-current || =fabric-sqldb

Modify unique constraints

[!INCLUDE sqlserver2016-asdb-asdbmi-fabricsqldb]

You can modify a unique constraint in [!INCLUDEssnoversion] by using [!INCLUDEssManStudioFull] or [!INCLUDEtsql].

Permissions

Requires ALTER permission on the table.

Use SQL Server Management Studio

Modify a unique constraint

  1. In the Object Explorer, right-click the table containing the unique constraint and select Design.

  2. On the Table Designer menu, select Indexes/Keys....

  3. In the Indexes/Keys dialog box, under Selected Primary/Unique Key or Index, select the constraint you wish to edit.

  4. Complete an action from the following table:

    To Follow these steps
    Change the columns that the constraint is associated with 1) In the grid under (General), select Columns and then select the ellipses (...) to the right of the property.

    2) In the Index Columns dialog box, specify the new column or sort order or both for the index.
    Rename the constraint In the grid under Identity, type a new name in the Name box. Make sure that your new name does not duplicate a name in the Selected Primary/Unique Key or Index list.
    Set the clustered option In the grid under Table Designer, select Create As Clustered and from the dropdown list choose Yes to create a clustered index and No to create a nonclustered one. Only one clustered index can exist per table. If a clustered index already exists in this table, you must clear this setting on the original index.
    Define a fill factor In the grid under Table Designer, expand the Fill Specification category and type an integer from 0 to 100 in the Fill Factor box.

  5. On the File menu, select Save table name.

Modify a unique constraint

To modify a UNIQUE constraint using Transact-SQL, you must first delete the existing UNIQUE constraint and then re-create it with the new definition.

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