Do all tables have primary key ?

Do all tables have primary key ?

select t.table_schema, t.table_name 
from information_schema.tables  t  
left join information_schema.statistics s         
on t.table_schema=s.table_schema and t.table_name=s.table_name and s.non_unique=0  
where s.table_name is null and t.table_schema not in ('mysql', 'information_schema','performance_schema');