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Need a Unique Constraint Example To Prevent Duplicates

Posted on 2009-04-14
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Last Modified: 2012-05-06
I have a table and I need to prevent duplicate rows on insert and update. The stipulations are as follows:
*The field DeptID can never contain a duplicate.
*Other fields such as contact or requestor may/will have duplicate data
*Need to avoid duplicate rows due to hitting submit twice or anything else a user might do.

Thanks in advance.
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Question by:JB4375
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chapmandew earned 2000 total points
ID: 24141181
alter table yourtablename
add constraint u_deptid unique (deptid)
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Expert Comment

by:Raja Jegan R
ID: 24141342
If DeptID Will / Should not contain Duplicates then you can have that as the primary key of the table right.
What's the use in having another column Sequence as a Primary key.
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by:chapmandew
ID: 24141402
Well, one thing is that it is a bad idea to have your clustered index on a column that is an nvarchar(50).

BTW...you really should consider designing your data types a little more carefully
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by:JB4375
ID: 24141526
@rrjegan17: DeptID will never have a duplicate, where as other fields may. Sequence is the primary key because I have updating turned on. I needed to have all fields editable in the event that someone made a mistake entering a Dept ID.
@Chapmandew: Not really sure about the "Clustered Index" or "Data Types" comment. I'm new to the SQL game. All of the data goes in as text, and I wanted to be sure I had enough room for anything that was entered.
I'm getting "Error Validating Constraint... Do you want to edit?
 
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Expert Comment

by:Raja Jegan R
ID: 24141550
<< "Error Validating Constraint... >>

That means you have data existing in that table and it violated the Unique constraint which you are trying to create.

Remove the duplicates in the existing data and try recreating it again.
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Expert Comment

by:chapmandew
ID: 24141552
did you enter the text in a new query window and run it exactly like I gave you?
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Author Comment

by:JB4375
ID: 24141805
I went to Design Table, Manage Constraints, Check Contraints Tab, New.
From there the Constraint Name is generated and there's a blank window for Constraint Expression.
I copied what you gave me in the window, and when I attempt to close it, that's when I get the error.
 
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Expert Comment

by:chapmandew
ID: 24141842
yeah, don't do that.  Just post what I gave you in a new query window, swap in your tables name, run it and you're done.
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Author Comment

by:JB4375
ID: 24141912
Ok... now I'm getting The Query Designer does not support the ALTER TABLE SQL construct.
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Expert Comment

by:chapmandew
ID: 24141935
i didn't say the query designer.  go to file, new, query.  paste the code I gave you in there.
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Author Comment

by:JB4375
ID: 24142018
I'm in SQL Server Entrprise Manager. When I select file, my choices are options --> disk cleanup, and exit. Any Query option I select takes me to Query Designer.
Sorry to be so clueless.
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Expert Comment

by:chapmandew
ID: 24142045
Ahh...thought you were in management studio.  No worries.  Open up query analyzer instead and give it a shot.
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Author Comment

by:JB4375
ID: 24142114
My bad.... We have both versions.... switched over to Management Studio, and it worked like a charm.
Thanks for your assistance, and infinite patience.
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Expert Comment

by:chapmandew
ID: 24142154
very welcome.
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