# Database Discussions > Microsoft SQL Server 2005 >  Replication Primary key

## bhosalenarayan

hello 
I am setting up transactional replication. And this is the first time I am doing this. I got to know that only the tables having primary key defined on them can be the part of this type of replication. But i am having hard time finding the reason that why is this so? I tried searching but everywhere it is given that it is mandatory but why it is mandatory is not given. So Can someone please let me know the reason for this.

Regards,
Narayan

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## rmiao

Sql is based on unique pkey values to apply transactions on subscriber.

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## bhosalenarayan

Thanks for ur reply!!! May be if u can elaborate a little, I ll get a better idea!!Thanks again

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## rmiao

Checked 'Advanced Replication Features and Internals' in books online?

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