Dynamic Change Column Values with NEW in Trigger Function - postgresql

Question

Is it possible to dynamically change column values in NEW with a Trigger Function?
Triggers:
CREATE TRIGGER lowercase_username_on_insert_trigger BEFORE INSERT OR UPDATE ON users
FOR EACH ROW EXECUTE PROCEDURE lowercase_on_insert('username');
CREATE TRIGGER lowercase_email_on_insert_trigger BEFORE INSERT OR UPDATE ON users
FOR EACH ROW EXECUTE PROCEDURE lowercase_on_insert('email');
Trigger Function:
CREATE OR REPLACE FUNCTION lowercase_on_insert()
RETURNS trigger
AS $lowercase_on_insert$
BEGIN
-- e.g., NEW.username = LOWER(NEW.username)
-- -OR- NEW.email = LOWER(NEW.email)
EXECUTE FORMAT('NEW.%s = LOWER(NEW.%s);', TG_ARGV[0], TG_ARGV[0]);
RETURN NEW;
END
$lowercase_on_insert$ LANGUAGE plpgsql;
I get an ERROR: syntax error at or new "NEW" whenever I run an INSERT.
This is my table:
CREATE TABLE users (
id BIGSERIAL PRIMARY KEY,
username VARCHAR(55) NOT NULL UNIQUE,
email VARCHAR(120) NOT NULL UNIQUE
);

Answer 1

Change your Trigger function as below
CREATE OR REPLACE FUNCTION lowercase() RETURNS trigger AS $$
BEGIN
NEW.username = LOWER(NEW.username);
NEW.email = LOWER(NEW.email);
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
and assign
CREATE TRIGGER tgrr BEFORE INSERT OR UPDATE ON users
FOR EACH ROW EXECUTE PROCEDURE lowercase();
OR
You can directly apply lower() function in Insert/Update like this
insert into users(username,email) values (lower('Jerry'),lower('JeRRY#mail.COM'));
update users set username=lower('JERRY'),email=lower('JERRY#MAIL.COM') where id =1