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Some sort of Informix equivalent of cksum on an SQL result

Posted on 2009-05-04
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Last Modified: 2013-12-24
I have a connection to a remote database that I want to regularly check for data changes. To determine whether there's been a change, I don't want to have to download the entire SQL result and compare it with the previous result.

What would solve my issue is the equivalent of the cksum command in linux, which gives a digital fingerprint of a file. That way, I would be able to just compare the fingerprint of the remote SQL with the fingerprint of the same SQL run on my local database, and download the full result when they differed.

One idea I had was something like a bitwise-sum of the md5 function result run on a column, but I'm not aware of Informix being able to manage a bitwise sum OR md5!

All suggestions appreciated, but yes I do know it would be lovely if there was a trigger on the remote table that updated a changedate upon changing... I can't change the remote database though.
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Question by:Terry Woods
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by:amrox
amrox earned 50 total points
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md5sum /path/to/database_file

should be available on most linux distros

perhaps store previous value and current value in seperate variables, and an if statement to compare?
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by:Terry Woods
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I need it to be done with SQL as I don't think I can get access to linux on the remote server.
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gheist earned 450 total points
ID: 24315378
select count(*);
select max(table.row_id)

Also you can set triger on update to emit dates of last change into side table.
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by:Terry Woods
ID: 24319974
Thanks - that would cover inserts and deletes.

However, I can't add a trigger, so do you know of any way to check for updates to the data?
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by:gheist
gheist earned 450 total points
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Indeed - if you hold DBA privilege you can add a trigger. There is no other way to check updates.
something like inserting or updating tablename,now() in some table
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by:Terry Woods
ID: 31577887
Thanks very much for your help!
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by:Terry Woods
ID: 24371885
Not the answer I wanted to hear, but still the correct one I believe! I'm crossing my fingers there are some on-update triggers on the tables I'm interested, but I suspect I'm out of luck.

Next best way to check for updates I think is selecting the minimum dataset possible (that I care about), and downloading it to my local server where I can compare it with a previously saved copy. It's a real shame the db engine can't do a checksum on the result of a select - it would save lots of trouble!
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Expert Comment

by:gheist
ID: 24372992
Some updates hit same page, some create new data page, so querying system statistics tables is not definite indicator also.
There is nothing wrong that each query is processed anew.
You can add your md5 checksum, that includes rowid also.
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