ORA-02266 solution

Action
A table has a PK (Primary Key)
B table has a FK (Foreign Key) and referenced to A table's PK

-> User tries to truncate table A

Error
ORA-02266: unique/primary keys in table referenced by enabled foreign keys

Solution I
Disable B table's FK
SQL> alter table HR.B disable constraint FK_B;
-- e.g. schema HR

Solution II
First truncate table B
SQL> truncate table B;

Then truncate table A
SQL> truncate table A;

How to disable/enable all triggers for tables?

Disable triggers for a table
SQL> alter table HR.TRG_EMPLOYEES disable all triggers;

Enable triggers for a table
SQL> alter table HR.TRG_EMPLOYEES enable all triggers;

Disable triggers belong to a schema (e.g. HR)
SQL>
DECLARE
   STR_EXEC   VARCHAR2 (1000);
BEGIN
   FOR cur_node IN (SELECT owner, table_name
                      FROM all_triggers
                     WHERE owner = 'HR')
   LOOP
      BEGIN
         str_exec :=
               'alter table '
            || cur_node.owner
            || '.'
            || cur_node.table_name
            || ' DISABLE ALL TRIGGERS';
         DBMS_OUTPUT.put_line (str_exec);

         EXECUTE IMMEDIATE str_exec;
      END;
   END LOOP;
END;
/

Enable triggers belong to a schema (e.g. HR)
SQL>
DECLARE
   STR_EXEC   VARCHAR2 (1000);
BEGIN
   FOR cur_node IN (SELECT owner, table_name
                      FROM all_triggers
                     WHERE owner = 'HR')
   LOOP
      BEGIN
         str_exec :=
               'alter table '
            || cur_node.owner
            || '.'
            || cur_node.table_name
            || ' ENABLE ALL TRIGGERS';
         DBMS_OUTPUT.put_line (str_exec);

         EXECUTE IMMEDIATE str_exec;
      END;
   END LOOP;
END;
/

ORA-01045 solution

Error
ORA-01045: user HR lacks CREATE SESSION privilege; logon denied

Solution
Grant CREATE SESSION privilege to 'HR' user
SQL> grant CREATE SESSION to HR;

ORA-28000 solution

Error
ORA-28000: the account is locked

Solution
Find the assigned profile for related user
SQL> select profile from DBA_USERS where username = 'HR';
-- e.g. DEFAULT

Disable failed_login_attempts parameter
SQL> alter profile "DEFAULT" limit failed_login_attempts UNLIMITED;

Check it
SQL> select resource_name,limit from dba_profiles where profile='DEFAULT';

Apply the new setting for user
SQL> alter user "HR" ACCOUNT UNLOCK;