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Editorial Team
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Asked: 2026-05-14T14:42:52+00:00

When I run this SQL statement: CREATE UNIQUE INDEX WordsIndex ON Words (Word ASC);

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When I run this SQL statement:

CREATE UNIQUE INDEX WordsIndex ON Words (Word ASC);

I get the following exception message:

The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name ‘dbo.Words’ and the index name ‘WordsIndex’. The duplicate key value is (ass).
The statement has been terminated.

The ‘Word’ column has a datatype of nvarchar(100).

There are two items in the ‘Word’ column that SQL Server interprets as the same: ‘aß’ and ‘ass’, which causes the indexing failure.

Why would SQL Server interpret those two different words as the same word?

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1 Answer

  1. Editorial Team

    The duplicate is due to the collation of the column. The following query will tell you the collation being used:

    Select COLLATION_NAME
From INFORMATION_SCHEMA.COLUMNS
Where TABLE_NAME = 'WordsIndex'
    And COLUMN_NAME = 'Words'

    In addition, in German, ‘ß’ is equivalent to ‘ss’. Thus, if you are using a Western European collation (e.g. SQL_Latin1_General_CP1_CI_AS), it will know that these are equivalent.

    http://en.wikipedia.org/wiki/%C3%9F

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