CREATE TABLE A
(
  IDE  NUMBER
);
Insert Into A Values(1);
Commit;

CREATE TABLE ORA_FAQ_ONE
(
  IDE   NUMBER,
  NAME  VARCHAR2(250 BYTE)
);
ALTER TABLE ORA_FAQ_ONE ADD (
  CONSTRAINT ORA_FAQ_ONE_PK PRIMARY KEY (IDE)

CREATE OR REPLACE TRIGGER TRG_ORA_FAQ_ONE BEFORE INSERT ON ORA_FAQ_ONE
 REFERENCING NEW AS NEW OLD AS OLD FOR EACH ROW
DECLARE
v_id NUMBER;
BEGIN
SELECT NVL(MAX(v_id),0)+1 INTO v_id FROM a;
:NEW.Ide:=v_id;
UPDATE a
SET ide=v_id;
END;

INSERT INTO ora_faq_one(name)
SELECT 'abc' FROM dual
UNION
SELECT 'def' FROM dual

SELECT NVL(MAX(v_id),0)+1 INTO v_id FROM a;

SELECT NVL(MAX(IDE),0)+1 INTO v_id FROM a;

SELECT IDE + 1 INTO v_id FROM a;

Update A
Set Ide=V_Id

Declare
Cursor C Is 
SELECT 'abc' Str FROM dual
UNION
SELECT 'def' FROM dual;
Begin
For V In C Loop
Insert Into Ora_Faq_One(Name) Values(V.Str);
End Loop;
End;

Insert Into Ora_Faq_One(Name)
Select 'Abc' From Dual
Union
Select 'Def' From Dual;

CREATE OR REPLACE TRIGGER trg_ora_faq_one   BEFORE INSERT
   ON ora_faq_one
   REFERENCING NEW AS NEW OLD AS OLD   FOR EACH ROW
DECLARE
   v_id   NUMBER;
BEGIN
   SELECT NVL (v_id, 0) + 1
     INTO v_id
     FROM a;

   DBMS_OUTPUT.put_line ('IDE WILL BE ===>' || v_id);
   :NEW.ide := v_id;
   
   UPDATE a
      SET ide = v_id;
END;

SQL> Declare
  2  Cursor C Is 
  3  SELECT 'abc' Str FROM dual
  4  UNION
  5  SELECT 'def' FROM dual;
  6  Begin
  7  For V In C Loop
  8  Insert Into Ora_Faq_One(Name) Values(V.Str);
  9  End Loop;
 10  End;
 11  /
Declare
*
ERROR at line 1:
ORA-00001: unique constraint (MICHEL.ORA_FAQ_ONE_PK) violated
ORA-06512: at line 8

SQL> create table t (id number, nam varchar2(50), ts timestamp default systimestamp);

Table created.

SQL> create or replace procedure p (id in number, nam in varchar2)
  2  is
  3     pragma autonomous_transaction;
  4  begin
  5    insert into t (id, nam) values (id, nam);
  6    commit;
  7  end;
  8  /

Procedure created.

SQL> CREATE OR REPLACE TRIGGER trg_ora_faq_one   BEFORE INSERT
  2     ON ora_faq_one
  3     REFERENCING NEW AS NEW OLD AS OLD   FOR EACH ROW
  4  DECLARE
  5     v_id   NUMBER;
  6  BEGIN
  7     SELECT NVL (v_id, 0) + 1
  8       INTO v_id
  9       FROM a;
 10  
 11     p(v_id, :new.name);
 12     :NEW.ide := v_id;
 13     
 14     UPDATE a
 15        SET ide = v_id;
 16  END;
 17  /

Trigger created.

SQL> Insert Into Ora_Faq_One(Name)
  2  Select 'Abc' From Dual
  3  Union
  4  Select 'Def' From Dual;
Insert Into Ora_Faq_One(Name)
*
ERROR at line 1:
ORA-00001: unique constraint (MICHEL.ORA_FAQ_ONE_PK) violated

SQL> select * from t;

        ID NAM        TS
---------- ---------- ------------------------------
         1 Abc        06-JUL-09 07.52.05.090000 AM
         1 Def        06-JUL-09 07.52.05.090000 AM

CREATE OR REPLACE TRIGGER trg_ora_faq_one
   BEFORE INSERT
   ON ora_faq_one
   REFERENCING NEW AS NEW OLD AS OLD
   FOR EACH ROW
DECLARE
   v_id   NUMBER;
BEGIN
   SELECT NVL (ide, 0) + 1
     INTO v_id
     FROM a;

   DBMS_OUTPUT.put_line ('IDE WILL BE ===>' || v_id);
   :NEW.ide := v_id;

   UPDATE a
      SET ide = v_id;
END;

CREATE OR REPLACE TRIGGER trg_ora_faq_one BEFORE INSERT ON ora_faq_one
 REFERENCING NEW AS NEW OLD AS OLD FOR EACH ROW
DECLARE
v_id NUMBER;
BEGIN
SELECT NVL(MAX(ide),0)+1 INTO v_id FROM Ora_Faq_One;
Dbms_Output.Put_Line('IDE WILL BE ===>'||v_id);
:NEW.Ide:=v_id;
END;

SQL> insert into ora_faq_one(name) values('asif');

1 row created.

SQL> insert into ora_faq_one(name)
  2  select 'Michle' From dual
  3  Union
  4  Select 'Asif' From Dual;
insert into ora_faq_one(name)
            *
ERROR at line 1:
ORA-04091: table MAMALIK.ORA_FAQ_ONE is mutating, trigger/function may not see it
ORA-06512: at "MAMALIK.TRG_ORA_FAQ_ONE", line 4
ORA-04088: error during execution of trigger 'MAMALIK.TRG_ORA_FAQ_ONE'

CREATE OR REPLACE TRIGGER trg_ora_faq_one BEFORE INSERT ON ora_faq_one
 REFERENCING NEW AS NEW OLD AS OLD FOR EACH ROW
DECLARE
v_id NUMBER;
BEGIN
SELECT NVL(MAX(ide),0)+1 INTO v_id FROM Ora_Faq_One;
Dbms_Output.Put_Line('IDE WILL BE ===>'||v_id);
:NEW.Ide:=v_id;
END;

SQL> insert into ora_faq_one(name) values('asif');

1 row created.

SQL> insert into ora_faq_one(name)
  2  select 'Michle' From dual
  3  Union
  4  Select 'Asif' From Dual;
insert into ora_faq_one(name)
            *
ERROR at line 1:
ORA-04091: table MAMALIK.ORA_FAQ_ONE is mutating, trigger/function may not see it
ORA-06512: at "MAMALIK.TRG_ORA_FAQ_ONE", line 4
ORA-04088: error during execution of trigger 'MAMALIK.TRG_ORA_FAQ_ONE'