I want to migrate data contained in an Oracle Table A to SQL Server. The table A contains a column CIN with unique constraint but mutliple null values. The problem is that SQL Server is rejecting the data. Is there any workaround for this ?
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@AaronBertrand, wasn't that just a few days ago? I had not seen that but yes, this appears to be a duplicate of that one.– Solomon RutzkyCommented Oct 28, 2014 at 15:13
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yes I think it's a duplicate :) the site didn't suggest that question to me..– mounaimCommented Oct 28, 2014 at 15:19
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1 Answer
You can use a Filtered Index to remove the NULL values from consideration regarding uniqueness. You would first drop the existing UNIQUE CONSTRAINT and then replace it with a UNIQUE INDEX. These two objects are essentially the same given that a UNIQUE CONSTRAINT actually exists via a UNIQUE INDEX (the documentation for creating a column constraint states that UNIQUE is a "constraint that provides entity integrity for a specified column or columns by using a unique index.").
CREATE UNIQUE NONCLUSTERED INDEX index_name
ON SchemaName.TableA (CIN ASC)
WHERE [CIN] IS NOT NULL;
answered Oct 28, 2014 at 14:42
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1Thank you @srutzky for the complete documentation of the answer :)– mounaimCommented Oct 28, 2014 at 15:08
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Thank you. It works. The importan thing is to drop the UNIQUE constrain on the columns definition and than create this filtered index. Commented Dec 7, 2021 at 10:44