Date: Fri, 20 May 2022 13:24:59 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: Chris Tsongas <chris.tsongas@gmail.com>
Cc: pgsql-novice@lists.postgresql.org
Subject: Re: Writing my first trigger
Message-ID: <20220520112459.GA20589@depesz.com>
Reply-To: depesz@depesz.com
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On Thu, May 19, 2022 at 11:18:48AM -0700, Chris Tsongas wrote:
> CREATE OR REPLACE FUNCTION update_employee() RETURNS TRIGGER AS $$
>   BEGIN
>     IF (OLD."preferredFirstName" IS NOT NULL) THEN
>       NEW."fullName" = OLD."preferredFirstName" || ' ' || OLD."lastName";
>     ELSE
>       NEW."fullName" = OLD."firstName" || ' ' || OLD."lastName";
>     END IF;
>     NEW."updatedAt" = now();
>     RETURN NEW;
>   END;
> $$ LANGUAGE plpgsql;
> 
> CREATE TRIGGER fullName
> INSTEAD OF INSERT OR UPDATE ON employee
>     FOR EACH ROW EXECUTE FUNCTION update_employee();

I'm not sure instead of trigger will do what you want. The tasks looks
much more like "before" trigger.

The whole if is not really needed. You can use coalesce:

NEW."fullName" := coalesce( NEW.preferredFirstName, NEW.firstName ) || ' ' || NEW.lastName;
RETURN NEW;

and really, really, really, read:
https://wiki.postgresql.org/wiki/Don't_Do_This#Don.27t_use_upper_case_table_or_column_names

depesz