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 unique key to existing column		  New Topic  Reply to Topic
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iceice
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5 Posts
Posted - 05/02/2012 :  10:04:32  Show Profile  Reply with Quote
table has primary key column and "orderid" nvarchar(30) column. table has many records. "orderid" column must be unique.
how to set this column as unique?

robvolk
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USA
15558 Posts
Posted - 05/02/2012 :  10:35:38  Show Profile  Visit robvolk's Homepage  Reply with Quote
If it's set at the primary key it's already unique.
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iceice
Starting Member

5 Posts
Posted - 05/02/2012 :  10:46:05  Show Profile  Reply with Quote
primary key column and "orderid" column are different. "orderid" column has null values too.
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robvolk
Most Valuable Yak

USA
15558 Posts
Posted - 05/02/2012 :  11:59:56  Show Profile  Visit robvolk's Homepage  Reply with Quote
Ah, misread the question. You can't put a unique constraint on orderid if it has multiple nulls. You either have to update them to be unique, delete them from the table, or create a unique filtered index:
CREATE UNIQUE INDEX ix_UNQ_orderID ON myTable(orderid) WHERE orderid IS NOT NULL
This will work on SQL Server 2008 or higher.
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