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Apply Unique constraints on existing database


Apply Unique constraints on existing database

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ashu.sajwan
ashu.sajwan
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I want to apply unique constraints on existing database,but column accepts null values how can i set unique constraints on that column without lose of data. helps me out
Adi Cohn-120898
Adi Cohn-120898
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I assume that you meant that the table should have many records with null value in this column, but the rest of the values should be unique. If I'm correct then you can try and use filtered unique index on that table (the filter would be of course on the null value).

Adi

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ashu.sajwan
ashu.sajwan
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Yes i need this thanks for your help
ashu.sajwan
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How can i do it with sql server 2005
GilaMonster
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With a hell of a lot of difficulty (and a computed column). The filtered index is 2008 and above, which since this was posted in the SQL 2008 forum we assumed you were using.

For 2005, define a computed column on ISNULL(<column that you want to be unique>,<the primary key column of the table>Wink and put a unique index on that computed column.


Gail Shaw
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ashu.sajwan
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Can i apply this approach for column which is varchar type?
GilaMonster
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Yes.


Gail Shaw
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TomThomson
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GilaMonster (2/17/2014)
Yes.

It's easier with varchar, nvarchar, and varbinary since it's generally not too difficult to convert the primary key to one of those types; other column types could be an issue.
And there's another complication - you need some way of ensuring that the value you convery the primary key into when the column in question has a null never clashes with some other value in that column, which may turn out to be nontrivial.

Tom

ashu.sajwan
ashu.sajwan
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I am creating CLUSTERED INDEX by running below query on sql server 2005

CREATE TABLE dbo.Example
(
col1 varchar(Max) NULL,
);
GO
CREATE VIEW dbo.ExampleUnique
WITH SCHEMABINDING AS
SELECT e.col1
FROM dbo.Example AS e
WHERE e.col1 IS NOT NULL;
GO
CREATE UNIQUE CLUSTERED INDEX cuq
ON dbo.ExampleUnique (col1);
GO

It shows error: Column 'col1' in table 'dbo.ExampleUnique' is of a type that is invalid for use as a key column in an index.

Any suggestions
ashu.sajwan
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Previous section is works fine when 'col1 int NULL'
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