Copy last row field value to another column table with trigger - postgresql

Question

I'm working in PostgreSQL using a trigger. I have 2 tables here, invoice_items and invoice. In the table 'invoice' data is inserted from the system, then the table 'invoice_items' is filled using a trigger to get the values from the inserted data of the table 'invoice'. Each insert from the system system consists of two rows like this:
table 'invoice':
id invoice_date statement amount
1 2018-10-03 Insert 5
2 2018-10-03 Update 6
then table 'invoice_items' after trigger the invoice data is inserted:
id total statement
1 5 Insert
2 6 Update
trigger:
create trigger do_fetch
after insert
on invoices
for each row
execute procedure insert_amount();
function insert_amount():
create function insert_amount()
returns trigger
language plpgsql
as $$
BEGIN
INSERT INTO invoice_items (total, statement) VALUES (new.amount, new.statement);
return null;
END;
$$;
But I just want to get last inserted data of 'invoices' to trigger 'invoice_items' to achieve a result like this:
id invoice_date statement amount
1 2018-10-03 Insert 5
2 2018-10-03 Update 6
id total statement
1 6 Update
I have tried to edit the trigger to this:
create constraint trigger do_fetch
after insert
on invoices
deferrable
for each row
execute procedure insert_amount();
but I still get 2 row inserted to 'invoice_items' table - not only the last row, any clue ? Thank you

Answer 1

Here is a example - you just need to adjust your sql with the desired tablenames and columnnames:
test=# create table bla1(ts timestamp, content text);
CREATE TABLE
test=*# create table bla1_log(ts timestamp, content text);
CREATE TABLE
test=*# create or replace function trg_bla1() returns trigger as $$begin insert into
bla1_log values (new.ts, new.content); return new; end; $$language plpgsql;
CREATE FUNCTION
test=*# create trigger trg1 after insert on bla1 for each row when (NEW.content =
'Update') execute procedure trg_bla1();
CREATE TRIGGER
test=*# insert into bla1 values (now(), 'bla');
INSERT 0 1
test=*# commit;
COMMIT
test=# insert into bla1 values (now(), 'Insert');
INSERT 0 1
test=*# commit;
COMMIT
test=# insert into bla1 values (now(), 'Update');
INSERT 0 1
test=*# select * from bla1;
ts | content
----------------------------+---------
2018-11-08 12:32:28.803439 | bla
2018-11-08 12:33:30.355516 | Insert
2018-11-08 12:33:38.451548 | Update
(3 rows)
test=*# select * from bla1_log ;
ts | content
----------------------------+---------
2018-11-08 12:33:38.451548 | Update
(1 row)
test=*#
EDIT:
As of your lack of replies and showing an effort to adjust your code according to my answer, I'm not sure if thats even worth my time - but here's what should work for you..
create table invoice(id serial, invoice_date text, statement text, amount integer);
create table invoice_items(id serial, total integer, statement text);
create or replace function insert_amount() returns trigger as $$begin
insert into invoice_items values (id, total, statement); return new; end;
create trigger mytrigger after insert on invoice for each row when (NEW.statement = 'Update') execute procedure insert_amount();