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Unique datatype in database

malik ge
Ranch Hand

Joined: May 13, 2011
Posts: 69
Hi,
I have a database in which I have make the userName field unique. So that only one userName exist in the database.
Now if user enters his information then How I can check that if the username already exists in the database?
Should I have to do:
and then compare the user Names with each other?
Or is there any other way to do this.
Thanks in advance...
Paul Clapham
Sheriff

Joined: Oct 14, 2005
Posts: 19728
    
  10

No, your query would be

and you would test to see if that query returned any records or not.

Don't be tempted to use string concatenation to create that query, though. Use a PreparedStatement and plug in the user ID via a parameter.
Scott Selikoff
author
Saloon Keeper

Joined: Oct 23, 2005
Posts: 3740
    
  10

Also, if you want to avoid case-insensitive differences, you might consider "lower(userID) = lower(?)". Granted, some databases can be configured to always perform case insensitive matching.

One issue with unique usernames is that even if you check ahead of time, a race condition could have two users creating the same record at the same time. It doesn't mean you shouldn't check ahead of time, you should always avoid throwing exceptions if they can be solved through application logic, but you should always have a pathway that handles when the database throws a uniqueness violation even after checking ahead of time.


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