How to kick off triggers without a seemly redundant update statement? - postgresql

Question

I have a simple table with a primary key, timestamp & count.
I have triggers to auto-update timestamp & count before the update event as is standard.
To execute the triggers, I have to execute an event (e.g. update). Although it works to perform the standard update, I'm not entirely comfortable with it as it seems redundant.
update users set username = 'johndoe' where username = 'johndoe';
Explicitly updating the fields would feel better from an SQL perspective but I'd rather leave the auto-updating to the triggers so the codebase is nicely separated from the schema implementation (for later upgrades).
Is there a way to kick-off all associated triggers on a table row without using update? Or is this an ok solution? Will a future database update refuse the transaction since nothing is changing?
Thanks!
/* update_timestamp function to call from trigger */
create function update_timestamp() returns trigger as $$
begin
NEW.timestamp := current_timestamp;
return NEW;
end;
$$ language plpgsql;
/* update_count function to call from trigger */
create function update_count() returns trigger as $$
begin
NEW.count := OLD.count + 1;
return NEW;
end;
$$ language plpgsql;
/* users table */
create table users(
username character varying(50) not null,
timestamp timestamp not null default current_timestamp,
count bigint not null default 1);
/* timestamp & count triggers */
create trigger users_timestamp_upd before update on users for each row execute procedure update_timestamp();
create trigger users_count_upd before update on users for each row execute procedure update_count();

Answer 1

Last question first:
Will a future database update refuse the transaction since nothing is changing?
No. This is perfectly valid SQL syntax. Refusing it would be going backwards in SQL Standard support, which is highly irregular for any production-ready RDBMS. Furthermore, the standard requires that BEFORE UPDATE triggers run on all affected rows, even if the rows have not actually changed.
Is there a way to kick-off all associated triggers on a table row without using update? Or is this an ok solution?
This is a reasonable solution so far as it goes, but I would call this a code smell. Triggers, in general, are not relational. A purely relational database is easier to reason about. In a purely relational database, you wouldn't be doing something like this. So you should ask yourself whether the triggers were a good idea to begin with. Of course, the answer may well be "yes, because there's no other reasonable way of doing this." But you should actually consider it, rather than just assuming this is the case.

Answer 2

Thanks. Decided to go with a function rather than triggers. Calling it directly from the PHP.
create or replace function add_update_user(varchar) returns void as $$
begin
if exists (select 1 from users where username = $1) then
update users set timestamp = current_timestamp where username = $1;
update users set count = count + 1 where username = $1;
else
insert into users (username) values ($1);
end if;
end;
$$ language plpgsql;
create table users(
username character varying(50) not null,
timestamp timestamp not null default current_timestamp,
count bigint not null default 1);
select add_update_user('testusername');