How to assign value to argument column name? - postgresql

Question

Here, we are trying to create common trigger function to all tables. we have to try pass an argument as column name(primary key column in table) to get the max value of that column in all tables. here the problem is we got the max of value of argument column but we can't assign the value to that argument column name.
declare
ll_maxid integer;
arg_column text :=TG_ARGV[0]::text;
begin
if TG_WHEN ='BEFORE' AND TG_OP='INSERT' THEN
execute format('SELECT coalesce(max(%s),0)+1 FROM %I.%I',arg_column,TG_TABLE_SCHEMA, TG_TABLE_NAME) INTO ll_maxid;
new.arg_column := ll_maxid;
end if;
return new;
end;
Error - The record new has no field 'arg_column'
how can I achieve this. I use PostgreSQL 13.2

Answer 1

I have yet to find a way to modify NEW in this manner in plpgsql. I can do it using plpython3u:
create table new_col_table (id integer, fld_1 integer, max_fld integer)
CREATE OR REPLACE FUNCTION public.new_col()
RETURNS trigger
LANGUAGE plpython3u
AS $function$
arg_column = TD['args'][0]
if TD['when'] == 'BEFORE' and TD['event'] =='INSERT':
plpy.notice("Value is " + arg_column)
rs = plpy.execute("select coalesce(max(fld_1), 0) as max_val from " + TD["table_schema"] + "." + TD["table_name"])
TD['new'][arg_column] = rs[0]['max_val']
return "MODIFY";
$function$
;
create trigger new_col_trg before insert on new_col_table for each row execute function new_col(max_fld);
insert into new_col_table values (1, 3, 3);
NOTICE: Value is max_fld
INSERT 0 1
insert into new_col_table values (2, 3, 0);
NOTICE: Value is max_fld
INSERT 0 1
select * from new_col_table ;
id | fld_1 | max_fld
----+-------+---------
1 | 3 | 0
2 | 3 | 3
select * from new_col_table ;