Question

I currently have a table with an id column that is being autoincremented and then there’s a tracking_code column that has a unique constraint on it.

Currently the tracking_code is being supplied by the person signing up, but now the client wants that tracking_code to be auto-generated yet be changeable as well.
In other words, where a user signs up, auto-generate the tracking_code, but allow the user to update that code to anything else as long as it stays unique.

Is it possible to do something like this in MySQL (append a string to an autoincremented id which only exists after the record is inserted) or is there another way of doing it in mysql:

INSERT INTO mytable (…, tracking_code, …) VALUES (…, ‘foo-‘ + id + ‘-bar’, …)

Answer 1

You can do this:

INSERT INTO mytable
  (..., tracking_code, ...)
VALUES (
  ...,
  CONCAT(
    'foo-',
    (
        SELECT
            AUTO_INCREMENT
        FROM
            information_schema.TABLES
        WHERE
            TABLE_SCHEMA = 'database'
        AND TABLE_NAME = 'mytable'
    ),
    '-bar'
  ),
  ...
)

Or

INSERT INTO mytable
SET tracking_code = CONCAT(
    'foo-',
    (
        SELECT
            AUTO_INCREMENT
        FROM
            information_schema.TABLES
        WHERE
            TABLE_SCHEMA = 'database'
        AND TABLE_NAME = 'mytable'
    ),
    '-bar'
),
...

Obviously only works if you have an AUTO_INCREMENT column.