is there anyway to add a primary autonumber key to an already existing database table

i have inherited a database application from someone else and there are a few table开发者_运维知识库s that dont have any primary keys. I want to add a new column into an already existing table and have it autonumber (starting from 1). how would i go about doing this?

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The SQL Server syntax is:

ALTER TABLE SomeTable ADD
    ID int NOT NULL IDENTITY(1, 1),
    CONSTRAINT PK_SomeTable PRIMARY KEY [NON]CLUSTERED (ID)