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DISTINCT KEYWORD for image data type column

Posted on 2011-03-08
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Last Modified: 2012-06-27
how want to use distinct key word for image datatype in sql server
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Question by:Kanigi
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by:jonaska
ID: 35068620
I would suggest calculating a checksum for the data, and select distinct on that. Maybe you can use a managed function to calculate the checksum?
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by:Kanigi
ID: 35068628
What is meant by calculating a checksum?
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by:jonaska
ID: 35068669
I thought of SHA1 or MD5 over the Image data.

In the below example MyManagedFucntion could simply return the checksum for the data in MyImageColumn.

SELECT MAX(idCol), dbo.MyManagedFucntion(MyImageColumn)  FROM myTable
GROUP BY dbo.MyManagedFucntion(MyImageColumn)

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Expert Comment

by:jonaska
ID: 35068679
Maybe this will explain better: http://en.wikipedia.org/wiki/Checksum
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Anthony Perkins earned 500 total points
ID: 35069188
You have a couple of options:
1.  As alluded to previously, use the HASHBYTES() function to get a hash of the image.
2. Use the undocumented function fn_varbintohexstr as in:
SELECT DISTINCT master.dbo.fn_varbintohexstr(YourColumnName)
FROM YourTableName

Both options have the caveat that they will only consider the first 8000 bytes.
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