How to get next alpha-numeric ID based on existing value from MySQL

Question

First, I apologize if this has been asked before - indeed I\'m sure it has, but I can\'t find it/can\'t work out what to search for to find it.

I need to generate un

Answer 1

How about this solution with a trigger and a table to hold the company_ref's uniquely. Made a correction - the reference table has to be MyISAM if you want the numbering to begin at 1 for each unique 4char sequence.

DROP TABLE IF EXISTS company;
CREATE TABLE company (
  company_name varchar(100) DEFAULT NULL,
  company_ref char(8) DEFAULT NULL
) ENGINE=InnoDB

DELIMITER ;;
CREATE TRIGGER company_reference BEFORE INSERT ON company
FOR EACH ROW BEGIN
   INSERT INTO reference SET company_ref=SUBSTRING(LOWER(NEW.company_name), 1, 4), numeric_ref=NULL;
   SET NEW.company_ref=CONCAT(SUBSTRING(LOWER(NEW.company_name), 1, 4), LPAD(CAST(LAST_INSERT_ID() AS CHAR(10)), 4, '0'));
END ;;
DELIMITER ;

DROP TABLE IF EXISTS reference;
CREATE TABLE reference (
company_ref char(4) NOT NULL DEFAULT '',
numeric_ref int(11) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (company_ref, numeric_ref)
) ENGINE=MyISAM;

And for completeness here is a trigger that will create a new reference if the company name is altered.

DROP TRIGGER IF EXISTS company_reference_up;
DELIMITER ;;
CREATE TRIGGER company_reference_up BEFORE UPDATE ON company
FOR EACH ROW BEGIN
   IF NEW.company_name <> OLD.company_name THEN
      DELETE FROM reference WHERE company_ref=SUBSTRING(LOWER(OLD.company_ref), 1, 4) AND numeric_ref=SUBSTRING(OLD.company_ref, 5, 4);
      INSERT INTO reference SET company_ref=SUBSTRING(LOWER(NEW.company_name), 1, 4), numeric_ref=NULL;
      SET NEW.company_ref=CONCAT(SUBSTRING(LOWER(NEW.company_name), 1, 4), LPAD(CAST(LAST_INSERT_ID() AS CHAR(10)), 4, '0'));
   END IF;
END;
;;
DELIMITER ;