The document discusses how to drop unique constraints in SQL Server using a stored procedure that queries the data dictionary for unique constraints on a specified table and column. It outlines a method for executing the drop action while noting a limitation that only applies to single-column unique constraints. Feedback from SQL procedure experts is encouraged to improve the method's functionality.

1. Generation 5 » Dropping Unique Constraints in SQL Server
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Dropping Unique Constraints in SQL Server
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The problem
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I got started with relational databases with mysql, so I’m in the habit of making
database changes with SQL scripts, rather than using a GUI. Microsoft SQL Server
requires that we specify the name of a unique constraint when we want to drop it. If
you’re thinking ahead, you can specify a name when you create the constraint; if
you don’t, SQL Server will make up an unpredictable name, so you can’t write a
simple script to drop the constraint.
A Solution
In the spirit of “How To Drop A Primary Key in SQL Server“, here’s a stored
procedure that queries the data dictionary to find the names of any unique constraint
on a specific table and column and drop them:
CREATE PROCEDURE [dbo].[DropUniqueConstraint]
@tableName NVarchar(255),
@columnName NVarchar(255)
AS
DECLARE @IdxNames CURSOR
SET @IdxNames = CURSOR FOR
select sysindexes.name from sysindexkeys,syscolumns,sysindexes
WHERE
syscolumns.[id] = OBJECT_ID(N'[dbo].['+@tableName+N']')
AND sysindexkeys.[id] = OBJECT_ID(N'[dbo].['+@tableName+N']')
AND sysindexes.[id] = OBJECT_ID(N'[dbo].['+@tableName+N']')
AND syscolumns.name=@columnName
AND sysindexkeys.colid=syscolumns.colid
AND sysindexes.[indid]=sysindexkeys.[indid]
AND (
SELECT COUNT(*) FROM sysindexkeys AS si2
WHERE si2.id=sysindexes.id
AND si2.indid=sysindexes.indid
)=1
OPEN @IdxNames
DECLARE @IdxName Nvarchar(255)
FETCH NEXT FROM @IdxNames INTO @IdxName
WHILE @@FETCH_STATUS = 0 BEGIN
DECLARE @dropSql Nvarchar(4000)
SET @dropSql=
N'ALTER TABLE ['+@tableName+ N']
DROP CONSTRAINT ['+@IdxName+ N']'
EXEC(@dropSql)
FETCH NEXT FROM @IdxNames
INTO @IdxName
END
CLOSE @IdxNames
DEALLOCATE @IdxNames
Usage is straightforward:
EXEC [dbo].[DropUniqueConstraint]
@tableName='TargetTable',
@columnName='TargetColumn'
This script has a limitation: it only drops unique constraints that act on a single
column, not constraints that act on multiple columns. It is smart enough, however,
to not drop multiple-column constraints in case one of them involves @columnName .
Feedback from SQL stored procedure wizards would be mostly certainly welcome.
Paul Houle on June 26th 2008 in SQL
Comments
http://gen5.info/q/2008/06/26/dropping-unique-constraints-in-sql-server/[1/16/2014 3:58:30 PM]
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2. Generation 5 » Dropping Unique Constraints in SQL Server
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http://gen5.info/q/2008/06/26/dropping-unique-constraints-in-sql-server/[1/16/2014 3:58:30 PM]