SELECT t.familyid,t.GroupID,cast((s.MaskNumber+t.MaskNumber) as nvarchar(200)) MaskNumber SELECT t1.familyid,t1.GroupID,cast((t1.MaskNumber) as nvarchar(200)) MaskNumber Insert into distinct m.familyid,m.GroupID,IIF(m.PortionKey='blank','',m.PortionKey) (200) NOT NULL INDEX IXkmask NONCLUSTERED) Where groupid =(select max(GroupID) from dbo.Partspc with(nolock)) SELECT t.familyid,t.GroupID,cast((s.PartNumber+ t.PartNumber) as nvarchar(200)) PartNumber SELECT t1.familyid,t1.GroupID,cast((t1.PartNumber) as nvarchar(200)) PartNumber Insert into distinct r.familyid,r.GroupID,IIF(r.PortionKey='blank','',r.PortionKey) ![]() (200) NOT NULL INDEX IXkpart NONCLUSTERED finding changed rows - they may skip some modifications.I work on SQL server 2012 I face issue I can't display Part Number with Mask related for family CREATE TABLE. Unfortunately, they are inappropriate for many applications e.g. If you decide to use CHECKSUM or BINARY_CHECKSUM in SQL Server, you must remember about the issues above. The same checksums mean nothing and collisions are not as rare as they seem to be. ![]() The same checksum does not imply the same inputĬhecksums can be used only in one direction - if the checksums are different, the inputs are different. The second text is not only different, it is even longer but the checksum is the same. declare nvarchar ( max ) = 'abcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyzabcdefghijklmnoprstuvwxyz' It means that only the first 255 characters have to be the same to give the same checksum. Would you like to learn Liquibase? Enroll to my course on Udemy.īINARY_CHECKSUM uses only first 255 characters of data that is varchar(max). What is interesting, if the number is an integer, the checksums are different. select binary_checksum (2, 2.1 ), binary_checksum (2, -2.1 ) One of the methods is changing a sign of a number with a decimal part. There are ways to build different inputs with the same checksum on purpose. The probability is not the worst problem of BINARY_CHECKSUM in my opinion. Moreover, the collision probability is pretty high as there are only 4 bytes for a checksum in SQL Server. Actually, for some (or even all) checksums there are infinite number of inputs that can be shortened to them using BINARY_CHECKSUM function. It must mean that many different inputs exist that produce the same checksum. For example 1024 bytes of information is shortened to 4 bytes (int). ![]() A checksum means shortening information from the input which is the same as loosing a part of it. The rows for which the previous and the current checksums are different, have changed.įrom mathematical point of view it is obvious that the same checksum does not imply identity of the rows. It should be enough to calculate a checksum for each row, save them somewhere and after a while do the same and compare the results. It seems like a perfect solution when you have a table with multiple columns and you need a way to easily check which rows changed or to find duplicates. If two sets have different checksums, it means that they are different. The idea is to shorten the input parameters to a single value that is easy to compare. For example: select checksum (2 ), checksum ( 'dfga', 4 ), checksum ( getDate (), 'OVdovudwkda4', 'ddsdg' ) And I do not only mean the collision probability! What is BINARY_CHECKSUMīoth CHECKSUM and BINARY_CHECKSUM calculate a checksum for a row or a list of values. This article shows how to use CHECKSUM and BINARY_CHECKSUM functions and why you should not rely on them. They could be very useful if they worked reliably. SQL Server has a few functions that allow calculating a hash from a single value or multiple values. Forget about BINARY_CHECKSUM in SQL Server!
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