Avoid increasing Auto_increment value?

问题

In MySQL, you can insert a row and update the 'last insert ID' at the same time. I'm using this trick to be able to insert items conditionally (uniqueness) and still get the unique ID in all cases.

The code below works. The problem is that the ON DUPLICATE KEY statement also updates the Auto_increment value. Is it possible to avoid that?

CREATE TABLE T(
    id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    X VARCHAR(64) NOT NULL UNIQUE
) ENGINE = InnoDB DEFAULT CHARSET=utf8;

INSERT INTO T(X) VALUES ('x') ON DUPLICATE KEY UPDATE id = LAST_INSERT_ID(id);
SELECT LAST_INSERT_ID();
INSERT INTO T(X) VALUES ('x') ON DUPLICATE KEY UPDATE id = LAST_INSERT_ID(id);
SELECT LAST_INSERT_ID();

Now we have one entry with id=1. However, the next entry will have id=3 since the Auto_increment value was updated when the second INSERT failed. This can be checked as follows:

SELECT Auto_increment FROM information_schema.tables WHERE table_name = 't'
     AND table_schema = DATABASE();

Q: Is it possible to use this trick (or equivalent) and keep the Auto_increment value? Obviously, in this case, it doesn't need to get updated.

来源：https://stackoverflow.com/questions/12692003/avoid-increasing-auto-increment-value