oracle中怎么给一个非自增的平常字段加一个唯一id规则，可以是按年月日拼上一个3位数或者六位数

create or replace package Pkg_Generate_Num is

-- Author  : ADMINISTRATOR
-- Created : 2012-12-28 7:18:36
-- Purpose :

-- 获取单据唯一编号
Function getVoucherNum(a_VoucherType varchar2) Return Varchar2;
Function getVoucherNum(a_VoucherType varchar2,a_len integer) Return Varchar2;
--技改工程保修中使用生成唯一编号
Function getVoucherNumBYJG(a_VoucherType varchar2) Return Varchar2;
end Pkg_Generate_Num;

create or replace package body Pkg_Generate_Num is

-- 获取记录唯一ID  生成如这样qz_201406120000000001
function getVoucherNum(a_VoucherType varchar2) return Varchar2 Is
pragma autonomous_transaction;
mN_LastUID  Varchar2(30);
mS_BillType Varchar2(30);
Begin
mS_BillType := a_VoucherType || to_char(Sysdate, 'yyyymmdd');

select Max_UID
into mN_LastUID
from sjt_MAXUID
Where bill_day = mS_BillType
for update;

mN_LastUID := mN_LastUID + 1;

UPDATE sjt_MAXUID
SET max_uid = mN_LastUID
Where bill_day = mS_BillType;
commit;
return mS_BillType || lpad(mN_LastUID, 10, '0');
exception
when NO_DATA_FOUND Then
Begin
Insert Into sjt_MAXUID
(bill_day, max_uid)
Values
(mS_BillType, 1);

commit;
return mS_BillType || lpad('1', 10, '0');
Exception
When Others Then
Rollback;
sys.dbms_lock.sleep(ceil(dbms_random.value*5));
Return getVoucherNum(a_VoucherType);
End;
end;

-- 获取记录唯一ID //输入的参数一个是前面添加的字符， 后面添加的是要生成几位数字
function getVoucherNum(a_VoucherType varchar2,a_len integer) return Varchar2 Is
pragma autonomous_transaction;
mN_LastUID  Varchar2(30);
mS_BillType Varchar2(30);
mS_len integer;
Begin
mS_BillType := a_VoucherType ;

select Max_UID
into mN_LastUID
from sjt_MAXUID
Where bill_day = mS_BillType
for update;

mN_LastUID := mN_LastUID + 1;

if a_len - length(mN_LastUID) < 0 then
mS_len := length(mN_LastUID);
else
mS_len := a_len;
end if;

UPDATE sjt_MAXUID
SET max_uid = mN_LastUID
Where bill_day = mS_BillType;
commit;
return mS_BillType || lpad(mN_LastUID, mS_len, '0');
exception
when NO_DATA_FOUND Then
Begin
Insert Into sjt_MAXUID
(bill_day, max_uid)
Values
(mS_BillType, 1);

commit;
return mS_BillType || lpad('1', a_len, '0');
Exception
When Others Then
Rollback;
sys.dbms_lock.sleep(ceil(dbms_random.value*5));
Return getVoucherNum(a_VoucherType);
End;
end;

-- 获取记录唯一ID生成如这样 qz_0001
function getVoucherNumBYJG(a_VoucherType varchar2) return Varchar2 Is
pragma autonomous_transaction;
mN_LastUID  Varchar2(30);
mS_BillType Varchar2(30);
Begin
mS_BillType := a_VoucherType;

select Max_UID
into mN_LastUID
from sjt_MAXUID
Where bill_day = mS_BillType
for update;

mN_LastUID := mN_LastUID + 1;

UPDATE sjt_MAXUID
SET max_uid = mN_LastUID
Where bill_day = mS_BillType;
commit;
return mS_BillType || '_' || lpad(mN_LastUID, 4, '0');
exception
when NO_DATA_FOUND Then
Begin
Insert Into sjt_MAXUID
(bill_day, max_uid)
Values
(mS_BillType, 1);

commit;
return mS_BillType|| '_' || lpad('1', 4, '0');
Exception
When Others Then
Rollback;
sys.dbms_lock.sleep(ceil(dbms_random.value*5));
Return getVoucherNum(a_VoucherType);
End;
end;

begin
-- Initialization
null;
end Pkg_Generate_Num;

-- Create table  SJT_MAXUID
create table SJT_MAXUID
(
bill_day VARCHAR2(20) not null,
max_uid  NUMBER(30)
)
tablespace USERS
pctfree 10
initrans 1
maxtrans 255
storage
(
initial 64
minextents 1
maxextents unlimited
);
-- Create/Recreate primary, unique and foreign key constraints
alter table SJT_MAXUID
add constraint PK_SJT_MAXUID_MAXUID primary key (BILL_DAY)
using index
tablespace USERS
pctfree 10
initrans 2
maxtrans 255
storage
(
initial 64K
minextents 1
maxextents unlimited
);