[dba-SQLServer] Update query leaves null

Haslett, Andrew andrew.haslett at ilc.gov.au
Mon Aug 14 04:32:19 CDT 2006


Why not just build a unique index / constraint on the existing 4 fields?

This will prevent duplicates from being created at all... 

-----Original Message-----
From: dba-sqlserver-bounces at databaseadvisors.com
[mailto:dba-sqlserver-bounces at databaseadvisors.com] On Behalf Of JWColby
Sent: Saturday, 12 August 2006 6:08 AM
To: dba-sqlserver at databaseadvisors.com
Subject: [dba-SQLServer] Update query leaves null

I need to build a new field on a table, and insert the first N
characters of Y other fields into that new field.  This will be known as
a match code and it is an accepted and known method in the client's
industry of weeding out duplicates.  For example I need to create a new
string with the first 5 characters of the first name, last name,
address1, address2, zip and the plus4.  I will write this new string
back into a new field.  What I want to do is to build a unique index on
the field.  Then as the update occurs, I need a silent failure if the
match code already exists.  Thus if the same exact match code is already
in the table, just leave a null of empty string in that match field for
the duplicate record.  Doing this would allow me to then go back and
delete the records where the match code is null and "de-dupe" the table.

If I do an update query in SQL, will it do this silent failure or will
it stop and announce the failure?  Do I need to do something specific to
get a "silent failure"?

John W. Colby
Colby Consulting
www.ColbyConsulting.com


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