About trigger

[cnplnsk]

i am giving whole program of trigger plz point out any error if there
this program is in file and called as trig2.sql

drop trigger trig2;
delimiter $$
create trigger trig2 after insert on tab for each row
first_block: begin
#declare cnt int default 0;
#declare off_set int default 3;
#declare continue handler for sqlstate 'HY000';
#drop trigger trig2;
insert into tab values(20,'New value');
end first_block;
$$
delimiter ;
insert into tab values(21,'value is 21');

but when i go to insert data in table it gives an error message

mysql> \. c:\sqldata\trig2.sql
Query OK, 0 rows affected (0.06 sec)

Query OK, 0 rows affected (0.00 sec)

ERROR 1442 (HY000): Can't update table 'tab' in stored function/trigger because
it is already used by statement which invoked this stored function/trigger.

so what should i do to solve this problem.
plz give reply right now.....