C# primary key

I would like to create unique identifier like below.

1. h111111

the format is
1. Must start "h"
2. with 5 numbers only

the 5 numbers can be random, but once it is created, it can't be duplicated.

is it possible?
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Pawan KumarDatabase ExpertCommented:
Yes possible..

SQL Solution , try

Pawan KumarDatabase ExpertCommented:
One more option for < SQL Server 2012

SELECT 'h' + CAST(CONVERT(NUMERIC(12,0),RAND() * 99999) + 10000 AS VARCHAR(7))
HuaMin ChenProblem resolverCommented:
By Unique constraint to the column, you can achieve this.
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Rajkumar GsSoftware EngineerCommented:
Since you have to generate next ID in a custom format, better go for sequence approach to make sure no duplicates.
Try any of the explained approach here
ITsolutionWizardAuthor Commented:
Can we use it without sql?
Pawan KumarDatabase ExpertCommented:
Try below options..

Random rnd = new Random();
        string str1 = "H" + rnd.Next().ToString().Substring(0, 5);

        char[] ch = Guid.NewGuid().ToString().Where(x => char.IsNumber(Convert.ToChar(x))).Take(5).ToArray();
        string str2 = "H" + (new string(ch));


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Pawan KumarDatabase ExpertCommented:
Yes you can also create unique constraints..Approach below.

DataTable at ;

UniqueConstraint aUnique =  new UniqueConstraint(
new DataColumn[] { at.Columns["ID"], at.Columns["Name"] });

Vitor MontalvãoMSSQL Senior EngineerCommented:
the 5 numbers can be random, but once it is created, it can't be duplicated.
Choose one of the above solutions to implement the generation of the values but to assure that's no duplicates you'll need to create an unique index on the field:
CREATE UNIQUE INDEX IndexName ON TableName (ColName)

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or create a Primary Key if you don't have one in the table:

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ITsolutionWizardAuthor Commented:
This is the best solution. Without using SQL is perfect. Good Job
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Microsoft SQL Server

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