auto_increment usage in composite key

问题

I am having a table with the composite key

emp_tbl(
companyId int not null,
empId int not null auto_increment,
name varchar2,
....
...
primary key(companyId,empId)
);

In mysql whats happening is while i starts inserting the data

Emp_tbl

companyId    empId
1             1
1             2
1             3
2             1
2             2

Note that when the companyId changes the auto_increament value is resetted to 1 again. I want to disable that. I mean i don't want to reset the auto_increament. I am expecting the result like this.

companyId    empId
1             1
1             2
1             3
2             4
2             5

Is it possible to do it? Thanks

回答1:

This is what happens with a composite primary key that incorporates a auto_increment. Recreate the primary key so that it's purely your auto_increment field (empId) then create a unique index on companyId and empId

EDIT

Note that this only applies to MyISAM and BDB tables. If you used InnoDB for your tables, then it would also work as you wanted

回答2:

If you do not want empId to reset then just reverse the order of primary definition

primary key(companyId,empId)

note that composite key order matters.

来源：https://stackoverflow.com/questions/3804845/auto-increment-usage-in-composite-key