如何基于Postgresql中的串行主键自动填充列？

Question

I have a table with columns like:

inner_id(serial pk) | id(varchar) | name(varchar) | fid(varchar) 

I want to send row with only id and name: (id, name) How can I say to Postgresql to complete 'fid' column with value based in serial pk(like string + primary key)? I want this kind of output:

inner_id(serial pk) | id(varchar) | name(varchar) | fid(varchar)
         1               G786k          NAME           FID-1
         2               l7hk           NAME           FID-2

AS a bonus I send row from python and have to use %s in query

UPD. I tried run query like:

INSERT INTO table (id, name, fid)
VALUES (%s,%s,%s||TO_CHAR(inner_id));

But I get an error, that i cannot refer to inner_id(primary key)

Answer 1

As your inner_id is a sequence, you can get the name of the sequence and use Nextval

So it should be something like

INSERT INTO TABLE ("id","name","fid")
VALUES (your_id, 'some_name', 'FID-' || nextval('your_sequence_id') - 1);

Answer 2

If you define inner_id as 'serial' Postgres will generate sequence for it. Generally something like "table_name_column_name-seq". You can then set the default for the "fid" column using the currval of that sequence.

create table soq.ref_to_id( inner_id serial, id text, name text, fid text);

alter table soq.ref_to_id alter column fid set default 'FID-' || currval('soq.ref_to_id_inner_id_seq')::text;

-- insert tast data    
insert into soq.ref_to_id(id, name)  
   values ('G786k', 'Gname')
        , ('17hk',  '17NAME');  

-- check results  
select * from soq.ref_to_id;