Question : add an auto-increment field and populate to an existing table with data

How do I add an auto-increment field, or identity seed to an existing table?  Does it have to be a primary key?

Answer : add an auto-increment field and populate to an existing table with data

The ALTER TABLE command will do it for you.  It not only adds the column, but when defined with the IDENTITY qualifier also populates it.

Below is a complete example.  The line you want to pay attention to is "ALTER TABLE ADD IDENTITY"
Remember that you must use a numeric or decimal data type with for identity columns with no decimal points.  These are the only "exact" datatypes in Sybase.

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create table fubar (col1 int, col2 varchar(32))
go

insert into fubar values (1,'one')
insert into fubar values (2,'two')
insert into fubar values (3,'three')
insert into fubar values (4,'four')
insert into fubar values (5,'five')
insert into fubar values (6,'six')
commit
go

select * from fubar
go

alter table fubar add col0 numeric(12) identity
go

select * from fubar
go