how to design a table in mysql with two auto_increment fields

Question

For a project we do the database design at the moment. We think we should use two auto_increment fields in one table.

table master:

`pid` int(10) NOT NULL auto_increment,
`iid` int(10) NOT NULL auto_increment,
...

To start with a alternate auto_incremet you can use ALTER TABLE tbl AUTO_INCREMENT = 100000; This will work only for the whole table 'tbl'. auto_increment for pid should be 50000000 and auto_increment for iid should be 80000000

We want to avoid splitting it into 3 tables with relations master -> table.pid and master -> table.iid.

altering the table is not working cause /* SQL Error (1075): Incorrect table definition; there can be only one auto column and it must be defined as a key */ /* SQL Error (1075): Incorrect table definition; there can be only one auto column and it must be defined as a key */

Is it possible or what alternative do you recommend?

Answer 1

If you cannot use two auto columns I think you must redesign your database. What do you need exactly?

Answer 2

I dont fully understand your question but you can use triggers to maintain key values like the following:

drop table if exists grid;
create table grid
(
grid_id int unsigned not null auto_increment primary key,
name varchar(255) not null,
next_token_id int unsigned not null default 0,
next_node_id int unsigned not null default 0
)
engine = innodb;

drop table if exists grid_token;
create table grid_token
(
grid_id int unsigned not null,
token_id int unsigned not null,
name varchar(255) not null,
primary key (grid_id, token_id) -- note clustered PK order (innodb only)
)
engine = innodb;

drop table if exists grid_node;
create table grid_node
(
grid_id int unsigned not null,
node_id int unsigned not null,
name varchar(255) not null,
primary key (grid_id, node_id) -- note clustered PK order (innodb only)
)
engine = innodb;

-- TRIGGERS

delimiter #

create trigger grid_token_before_ins_trig before insert on grid_token
for each row
begin

declare tid int unsigned default 0;

  select next_token_id + 1 into tid from grid where grid_id = new.grid_id;
  set new.token_id = tid;
  update grid set next_token_id = tid where grid_id = new.grid_id;

end#

create trigger grid_node_before_ins_trig before insert on grid_node
for each row
begin

declare nid int unsigned default 0;

  select next_node_id + 1 into nid from grid where grid_id = new.grid_id;
  set new.node_id = nid;
  update grid set next_node_id = nid where grid_id = new.grid_id;

end#

delimiter ;

-- TEST DATA

insert into grid (name) values ('g1'),('g2'),('g3');

insert into grid_token (grid_id, name) values
(1,'g1 t1'),(1,'g1 t2'),(1,'g1 t3'),
(2,'g2 t1'),
(3,'g3 t1');

insert into grid_node (grid_id, name) values
(1,'g1 n1'),(1,'g1 n2'),
(2,'g2 n1'),
(3,'g3 n1'),(3,'g3 n2');

select * from grid;
select * from grid_token;
select * from grid_node;