How to find Primary Key of a table

 

SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner FROM all_constraints cons, all_cons_columns cols WHERE cols.table_name = 'TABLENAME' AND cons.constraint_type = 'P' AND cons.constraint_name = cols.constraint_name AND cons.owner = cols.owner AND cols.owner = 'sivaora' AND cons.owner = 'sivaora' ORDER BY cols.table_name, cols.position

This can be useful when getting error
ORA-00001: unique constraint (constraint_name) violated