Postgresql insert trigger to concatenate

Question

I want to create a trigger to concatenate my column with event "before insert", but the query didn't work and i got an error:

SQL error:

ERROR: syntax error at or near "SET" LINE 4: SET new.fullname = CONCAT(new.first_name, '', new.mid_name, ...

In statement:
CREATE TRIGGER insert_trigger
BEFORE INSERT ON t_employees
FOR EACH ROW
SET new.fullname = CONCAT(new.first_name, '', new.mid_name, '', new.last_name);

Answer 1

Here's a working solution:

CREATE TEMPORARY TABLE t_employees (
    first_name TEXT,
    mid_name TEXT,
    last_name TEXT,
    fullname TEXT
);

CREATE OR REPLACE FUNCTION set_fullname()
    RETURNS TRIGGER AS $$
    BEGIN
        NEW.fullname = NEW.first_name || ' ' || NEW.mid_name || ' ' || NEW.last_name;
        RETURN NEW;
    END;
    $$ language 'plpgsql';


CREATE TRIGGER set_fullname_trigger
    BEFORE INSERT OR UPDATE ON t_employees
    FOR EACH ROW
    EXECUTE PROCEDURE set_fullname();


SET client_min_messages TO 'debug';
INSERT INTO t_employees VALUES ('fname1', 'mname1', 'lname1');
SELECT * FROM t_employees;
UPDATE t_employees SET first_name = 'updated-first-name';
SELECT * FROM t_employees;

Answer 2

Well, i finally did it. According your suggestions and postgresql docs i've made the trigger like what i want. Here is the syntax:

create the function:

 CREATE FUNCTION insert_funct() RETURN TRIGGER AS 
    $$
    BEGIN
      SELECT new.fullname := CONCAT(new.first_name, '', new.mid_name, '', new.last_name);
    END;
    $$
    LANGUAGE plpgsql;

then create the trigger:

CREATE TRIGGER insert_trigger
  BEFORE INSERT ON t_employees
  FOR EACH ROW
EXECUTE PROCEDURE insert_funct();