increment field in mysql

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MySQL

Hello all,

i have a databse in mysql named as"dbtrial" and in this database i have a table named as"test"
in test table i have only two coloumns "BranchId","BranchName" where BranchId is the primary key
i want tha every time i enter the records the BranchId field should be incremented by 1. for this i write a code which is as follows........

use dbtrial;
create procedure sp_insert5
(
 in branchid int(11),
in branchname varchar(50)
)
 select max(branchid)+1  into @branchid from test;
insert into test (branchid,branchname)
values(branchid,branchname);
call sp_insert5(
'zeroerror1')

but i got the proble when i run it


(0 row(s)affected)
(0 ms taken)

Error Code : 1062
Duplicate entry '0' for key 'PRIMARY'
(0 ms taken)

i dont want to use autoincrement.
please help me out

thanks and regard
subiya