Its my first time using SQL and I am having trouble with the ADD CONSTRAINT command. I am trying to add a constraint to a column that refers back to the primary key of the table that the column is in.

Here's what I have:

create table project
(p_id NUMBER(6) constraint project_p_id_pk primary key,
project_name VARCHAR2(30),
client_id NUMBER(6),
mgr_id NUMBER(6),
parent_p_id NUMBER(6),
constraint project_client_id_fk foreign key (client_id)
references client (client_id),
constraint project_mgr_id_fk foreign key (mgr_id)
references consultant (c_id));

alter table project
add constraint project_p_id_fk
foreign key (parent_p_id)
references project (p_id);

I want to make project_p_id refer to p_id, but I'm getting this error
ORA-00904: invalid column name at line 3
line 3 being "foreign key (parent_p_id)"

Oh and here is a line from my assignment saying what we have to do:
"parent_p_id references the same table project. Note that you need to use ALTER statement to create this foreign key."

Anyway I'm sure I have made a simple error or something seein as how this is my first time. Thx fer the help.

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[This message has been edited by spamjedi (edited February 02, 2002).]