Creating a trigger to copy data from 1 table to another - sql

Question

I am trying to create a trigger that will copy data from table 1 when and paste it into table 2, when a new entry has been put into table 1:
Table 1
id | first_name | last_name | email | uid | pwd
----+------------+-----------+-------+-----+-----
Table 2
user_id | user_first_name | user_last_name | user_uid
---------+-----------------+----------------+---------
the code i am using is this :
DROP TRIGGER IF EXISTS usersetup_identifier ON users;
CREATE OR REPLACE FUNCTION usersetup_identifier_insert_update() RETURNS trigger AS $BODY$
BEGIN
if NEW.identifier is null then
NEW.identifier := "INSERT INTO users_setup (user_id, user_first_name, user_last_name, user_uid)
SELECT id, first_name, last_name, uid
FROM users";
end if;
RETURN NEW;
end
$BODY$
LANGUAGE plpgsql;
CREATE TRIGGER usersetup_identifier
AFTER INSERT OR UPDATE ON users FOR EACH ROW
EXECUTE PROCEDURE usersetup_identifier_insert_update();
but when i insert data into table 1 i am getting this error message :
NOTICE: identifier "INSERT INTO users_setup (user_id, user_first_name, user_last_name, user_uid)
SELECT id, first_name, last_name, uid
FROM users" will be truncated to "INSERT INTO users_setup (user_id, user_first_name, user_last_na"
ERROR: record "new" has no field "identifier"
CONTEXT: SQL statement "SELECT NEW.identifier is null"
PL/pgSQL function usersetup_identifier_insert_update() line 3 at IF
the table descriptions are:
Table "public.users"
Column | Type | Collation | Nullable | Default
------------+---------------+-----------+----------+-----------------------------------
id | integer | | not null | nextval('users_id_seq'::regclass)
first_name | character(20) | | not null |
last_name | character(20) | | not null |
email | character(60) | | not null |
uid | character(20) | | not null |
pwd | character(20) | | not null |
Indexes:
"users_pkey" PRIMARY KEY, btree (id)
"users_email_key" UNIQUE CONSTRAINT, btree (email)
"users_pwd_key" UNIQUE CONSTRAINT, btree (pwd)
"users_uid_key" UNIQUE CONSTRAINT, btree (uid)
Triggers:
usersetup_identifier AFTER INSERT OR UPDATE ON users FOR EACH ROW EXECUTE PROCEDURE usersetup_identifier_insert_update()
All the columns match there corresponding columns
can any one help and tell me where i am going wrong?
Table "public.users_setup"
Column | Type | Collation | Nullable | Default
-----------------+------------------------+-----------+----------+-----------------------------------------
id | integer | | not null | nextval('users_setup_id_seq'::regclass)
user_id | integer | | |
user_first_name | character(20) | | |
user_last_name | character(20) | | |
user_uid | character(20) | | |
Can any one help me with where I am going wrong?

Answer 1

There are multiple errors in your code
the table users has a column named identifier so the expression NEW.identifier is invalid
You are assigning a value to a (non-existing) column with the expression new.identifier := ... - but you want to run an INSERT statement, not assign a value.
String values need to be enclosed in single quotes, e.g. 'Arthur', double quotes denote identifiers (e.g. a table or column name). But there is no column named "INSERT INTO use ..."
To access the values of the row being inserted you need to use the new record and the column names. No need to select from the table:
As far as I can tell, this is what you want:
CREATE OR REPLACE FUNCTION usersetup_identifier_insert_update()
RETURNS trigger
AS
$BODY$
BEGIN
INSERT INTO users_setup (user_id, user_first_name, user_last_name, user_uid)
values (new.id, new.first_name, new.last_name, new.uid);
RETURN NEW;
end
$BODY$
LANGUAGE plpgsql;
Unrelated, but:
copying data around like that is bad database design. What happens if you change the user's name? Then you would need to UPDATE the user_setup table as well. It is better to only store a (foreign key) reference in the user_setup table that references the users table.