Question

I have a table member. I want to make an user id using auto increment.
I have tried using the following:

SET new.user_id = CONCAT(new.name, LPAD((SELECT AUTO_INCREMENT FROM 
information_schema.TABLES WHERE
TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'member'),3,'0'));

But when I inserted a new member, i’ve got an error message user_id cannot be null and the data wasn’t added. I want the user id will shown like jos001 as an primary key.

Please help me.. how to make it happen?

Answer 1

Try this BEFORE INSERT trigger –

Full script:

CREATE TABLE member(
  user_id VARCHAR(23) NOT NULL,
  name VARCHAR(20) DEFAULT NULL
);

DELIMITER $$

CREATE TRIGGER trigger1
  BEFORE INSERT
  ON member
  FOR EACH ROW
BEGIN

  -- Find next id for new user - MAX+1
  SELECT MAX(CAST(SUBSTRING(user_id, LENGTH(user_id) - 2, 3) AS SIGNED)) + 1 INTO @next_id
    FROM member WHERE SUBSTRING(user_id, 1, LENGTH(user_id) - 3) = NEW.name;

  SET NEW.user_id = CONCAT(NEW.name, LPAD(IFNULL(@next_id, 1), 3,'0'));
END$$

DELIMITER ;

Insert some records:

INSERT INTO member VALUES('', 'jos');
INSERT INTO member VALUES('', 'jos');
INSERT INTO member VALUES('', 'jos');
INSERT INTO member VALUES('', 'alex');
INSERT INTO member VALUES('', 'alex');
INSERT INTO member VALUES('', 'jos');

Check result:

SELECT * FROM member;

+---------+------+
| user_id | name |
+---------+------+
| jos001  | jos  |
| jos002  | jos  |
| jos003  | jos  |
| alex001 | alex |
| alex002 | alex |
| jos004  | jos  |
+---------+------+