I use checksum in SQL Server to distinguish between records that are different instead of comparing the character strings in them. My application was working fine until I added a lot of records and suddenly things started getting messy. After taking a look at it I determined the issue was that the checksums were being computed as being equal even though the columns had different values. Here is one example:
select checksum('where myval in (7004054,7004055)') a, checksum('where myval in (7003888,7003889)') b
Notice that the two values are the same even though the where clause is very different. There was an easy fix in my case though:
select checksum(N'where myval in (7004054,7004055)') a, checksum(N'where myval in (7003888,7003889)') b
So in this case I only had to change the variables I used to calculate the checksums from varchar to nvarchar and everything started working. This is going to force me to take a much closer look at my process though.
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