更新mysql表。 一个字段= old_value - 1

Question

What I need to do is: - Delete one entry from table formfields - Update EVERY field with ordering > (ordering of the deleted field) - Set the ordering of the updated fields to the current value minus 1 (eg if current ordering on the field is 8, then it should be set to 7).

Is that possible in one query? Or how can I make it happen?

Answer 1

You can set up a transaction to do this all at once.

Given the following table:

CREATE TABLE `formfields` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(25) NOT NULL,
  `order_no` int(11) NOT NULL,
  PRIMARY KEY (`id`)
);

You can do something like the following:

START TRANSACTION;
DELETE FROM formfields WHERE order_no = {YOUR_NUM};
UPDATE formfields SET order_no = order_no - 1 WHERE order_no > {YOUR_NUM};
COMMIT;

Answer 2

You obviously can't do the DELETE and the UPDATE in the same query, but you could use InnoDB, start a transaction, run the delete query and then use an update query such as...

UPDATE formfields SET field_value = field_value - 1 
WHERE field_value >= <VALUE YOU'VE JUST DELETED>

...prior to committing the transaction.

Doing the two queries back to back using a MyISAM table will work nine times out of ten (depending on load, etc.), but you really shouldn't go there.