sql server programming: On 4=D4=C211=C8=D5, =C9=CF=CE=E79=CA=B157=B7=D6, lucius <luc...@newsgroup.n=
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Yes,i think you can all a timestamp column.this column will update
whenever you update one row or insert one row.

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Uri,

Can you describe checksum, checksum_agg functions in brief.
I already check BOL, but really i have not understood that points.

Rahul

I would like to determine if a table has had any changes to any row
since the last time I checked. The table undergoes a heavy series of
updates at irregular times (a result of a seperate batch system), and
I would like to quickly poll the table every n minutes to see if
things have happened to it. Is that possible?

Thanks.

Hi
checksum
This function computes hash value. I used '*' as argument to meant that
computation is over all the columns of the table.
checksum_agg functions
This function returns checksums in groups as BOL describes it. If something
has changed in the table then checksum's value will be changed also


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Rahul,

You will notice that Uri's first sample said that if the checksums were
equal they were "probably the same". You need to determine if 'probably' is
good enough for your needs.

This is because a checksum is only an integer and because the algorithm uses
Exclusive ORs it is fairly easy for non-identical data to result in
identical checksums. If you Google around there are examples of this
problem, including this simple example from David Portas:
SELECT BINARY_CHECKSUM('ABA'), BINARY_CHECKSUM('ACQ')


Result:

----------- -----------
17761 17761

RLF

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Hi
if (select checksum_agg(checksum(*)) from t1)
<> (select checksum_agg(checksum(*)) from t2)
print 'different'
else
print 'probably the same'




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Hi, Lucius,

It is a good way to combine Yuanbo and Russel's suggestions together. Could
you please let me know if you need furhter assistance on this issue?

Have a good day!

Best regards,
Charles Wang
Microsoft Online Community Support
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