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Apply Unique constraints on existing database


Apply Unique constraints on existing database

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TomThomson
TomThomson
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ashu.sajwan (2/17/2014)
...
col1 varchar(Max) NULL,
...
CREATE UNIQUE CLUSTERED INDEX cuq
ON dbo.ExampleUnique (col1);

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

The reason for the failure is that columns of lob type (nvarchar(max), varchar(max), varbinary(max), ntext, text, image) can't be key columns in an index. So for example varchar(768) is OK, but varchar(MAX) isn't.

Incidentally, I think this is a very good technique given that your version of SQL Server doesn't support filtered indexes.

Tom

ashu.sajwan
ashu.sajwan
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Your suggestion works for me
Thanks Tom
GilaMonster
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Why clustered? This isn't typically where you would put the clustered index.


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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ashu.sajwan
ashu.sajwan
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Can you please share other approach to do this easiest way in sql server 2005?
GilaMonster
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I already did.

GilaMonster (2/17/2014)
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
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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ashu.sajwan
ashu.sajwan
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Can you explain it as in sql form as below


CREATE TABLE dbo.Example
(
col1 varchar(100) 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
GilaMonster
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Why a view, rather than just an indexed computed column? It'll work, but....

Do you not have a column that is already unique in the table, eg the primary key columns?


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
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ashu.sajwan
ashu.sajwan
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Can you mention a example or a dummy script which create a indexed computed column?
ashu.sajwan
ashu.sajwan
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Below script will work in this case or not

CREATE TABLE TEST_UQ (COL1 INT IDENTITY(1,1) PRIMARY KEY, COL2 VARCHAR(10) NULL,COL3 AS (CASE WHEN COL2 IS NULL THEN CAST(COL1 AS VARCHAR(10)) ELSE COL2 END))
GO

CREATE UNIQUE INDEX TEST_UQ_IND_1 ON TEST_UQ (COL3)
GO

This also works for in my case
GilaMonster
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Yup, that's it. Should be less overhead than an indexed view.


Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
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