Altering table error

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I'm trying to alter an existing table, whith data in it, adding a column
called "cap_id" that should be a "serial" or "serial8" type, but when I
try to do it I receive the next message:

| provesmasis-# provesmasis=# alter table captrajectes add column cap_id
serial;
| NOTICE:  ALTER TABLE will create implicit sequence
'captrajectes_cap_id_seq' for SERIAL column 'captrajectes.cap_id'
| NOTICE:  ALTER TABLE / ADD UNIQUE will create implicit index
'captrajectes_cap_id_key' for table 'captrajectes'
| ERROR:  parser: parse error at or near "notice"
| provesmasis=# NOTICE:  ALTER TABLE will create implicit sequence
'captrajectes_cap_id_seq' for SERIAL column 'captrajectes.cap_id'
| provesmasis-# NOTICE:  ALTER TABLE / ADD UNIQUE will create implicit
index 'captrajectes_cap_id_key' for table 'captrajectes'
| provesmasis-# ERROR:  Adding columns with defaults is not implemented.
| provesmasis-#         Add the column, then use ALTER TABLE SET DEFAULT.

What am I doing wrong?

Thanks in advance for your answer.

Josep Sànchez
~ [papapep]

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