altering a table to set serial function

Dear my friends...

I am using postgres 7.4 and SuSE 9.1.

I want to use auto_increment as on MySQL. I look up
the documentation on www.postgres.com and I found
"serial" .

But I don't know how to create auto_increment.
here is my try:
"
kv=# alter table sales alter column salesid int4
serial;
ERROR:  syntax error at or near "int4" at character 40
"

Please tell me the correct command to that.

Thank you very much in advance.



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