MySQL-AUTO_INCREMENT，表的自定义增量开始和值

Question

Is there a way to specify a custom auto increment starting value and a custom auto increment increment value for only one MySQL table?

I couldn't find a clear answer to my question. There seem to be two global variables auto_increment_increment and auto_increment_offset but I need it for one table only. Another site suggested using AUTO_INCREMENT(<offset>,<increment>) but this approach just triggered MySQL errors.

So is there a way to do this?

Answer 1

You can't change the step on a per table basis in MySQL. Running SET @@auto_increment_increment=2; or changing the startup value will affect all tables and databases on the server.

As far as I can tell you have two options:

1. Disable MySQL's auto_increment and create some php function that does this for you, though I wouldn't recommend this unless it's a very low transaction site.

2. You could consider a trigger that performs the maths you want and sets a custom value to another field.

   CREATE TRIGGER trigger BEFORE INSERT ON my_table FOR EACH ROW BEGIN
   SET NEW.id2 = NEW.id * 2;
   END

Answer 2

You can execute this SQL, say if you wanted to start it at 3:

ALTER TABLE foo AUTO_INCREMENT = 3;

As others pointed out, I don't believe you can do both, however.

Answer 3

You can change the current value to be applied to the next inserted row via:

ALTER TABLE table AUTO_INCREMENT = ?;

The increment value can be set via the auto_increment_increment server variable.

Unfortunately this will effect all databases/tables on the server if set in Global context.

You can set this variable on a session-specific basis. So, if you wanted to use a specific set of DB connections, to which you set the value on a session basis, that is possible. This might be a bit unwieldy to manage as you would, in essence, need a distinct connection (or pool of connections) just to update this single table.

Answer 4

I have found the way to change auto_increment, just alter table. I have to the problem when migrate old database to new system (from Heroku to Amazon), but have to keep all old data (not change id), but every day a hundred thousand happen, so how can I keep data and duplicate data do not happen, what I did:

1. Turn off auto increment in new system database (Amazon)
2. Write script set offset in new system (Aamzon) begin from 1.000.000
3. Write script export data from old system (Heroku)
4. Write script impport data to new system by this way they will keep all data without change any offet
5. Turn on auto increment
6. Done.

Ex:

- Create table:
CREATE TABLE `test`.`table_inc` (
  `idtable_inc_id` INT NOT NULL AUTO_INCREMENT,
  `table_inccol` VARCHAR(45) NULL,
  PRIMARY KEY (`idtable_inc_id`));

- Alter table (to remove auto increment)
ALTER TABLE `test`.`table_inc` 
CHANGE COLUMN `idtable_inc_id` `idtable_inc_id` INT(11) NOT NULL ;

Answer 5

I have found another answer for this solution

> mysqldump -u root -p database_heroku | sed 's/ AUTO_INCREMENT=[0-9]*\b/ AUTO_INCREMENT=1100001/'  > /new_increment_with_data_heroku_database.sql

Ref: http://melikedev.com/2011/06/01/mysql-remove-auto_increment-from-schema-dumps-mysqldump/