How to find tables without a primary key in Oracle

Left join DBA_TABLES against DBA_CONSTRAINTS filtered to constraint_type = P; NULL rows are tables with no primary key. Handy audit before enabling GoldenGate, materialized view replication, or any tool that relies on unique row identity.

SELECT t.owner AS schema_name,
       t.table_name
FROM   sys.dba_tables t
LEFT JOIN sys.dba_constraints c
       ON t.owner           = c.owner
      AND t.table_name      = c.table_name
      AND c.constraint_type = 'P'
WHERE  c.constraint_type IS NULL
ORDER BY t.owner, t.table_name;