can we use more than one primary keys in a mysql table

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C#

MySQL

hello

i have create one table with one column as primary key, now i wanted to alter the column by adding the serialno/index column by auto_increment type in mysql by using the code
alter table tablename add columnname int auto_increment first,primarykey(columnname);
so is there any problem in having more than one primary key in a table

Please replay me

Regards
Ginnas