关于数据库查询优化的一个例子（责任中心例子）

CREATE OR REPLACE FUNCTION "GET_EMPCENTER"(PI_EMPOID Number,
PI_GROUP Number,
PI_UNITID Number,
PS_YEAR Varchar2,
PS_MONTH Varchar2,
PS_DELIVERNUM Number)
--返回交流、挂职类人员所对应的成本部门（不一定是责任中心）

Return Number Is

li_unit1 Number := 0;
ls_date1 Char(6);
ls_month1 Char(3);
li_count1 Number;
ls_date Char(6);
ls_month Char(3);
li_count Number;
li_dutycenter Number := 0; --财务责任中心
li_orgunit Number := 0; --财务机构
li_id Number;
li_pid Number;
li_parentorgunit Number := 0; --机构oid

Begin

-- 先判断发放记录表中是否已经插入过本发放月的本员工 如果以后反映效率低，此处，以及以后的count(*)都可以改为使用游标代替，可以减少一半的查询量

select Count(*)
into li_count1
from tb_cnb_dutycenterjudge pay
where pay.c_month = PS_MONTH
and pay.c_year = PS_YEAR
and pay.c_unitid = PI_UNITID
and pay.c_groupid = PI_GROUP
and pay.c_empoid = PI_EMPOID
and pay.c_delivernum = PS_DELIVERNUM;

if li_count1 > 0 then

select pay.c_payunitid
into li_dutycenter
from tb_cnb_dutycenterjudge pay
where pay.c_month = PS_MONTH
and pay.c_year = PS_YEAR
and pay.c_unitid = PI_UNITID
and pay.c_groupid = PI_GROUP
and pay.c_empoid = PI_EMPOID
and pay.c_delivernum = PS_DELIVERNUM
and rownum = 1;

return li_dutycenter;
end if;

ls_month1 := '0' || ps_month;
ls_date1 := ps_year || substr(ls_month1, length(ls_month1) - 1);

--判断是否在个人责任中心中维护，如未维护则直接返回员工所在部门
Select Count(*)
Into li_count1
From TB_CNB_EMPDUTY
Where C_EMPID = PI_EMPOID
And C_GROUPID = PI_GROUP
And C_EFECTIVETIME <= ls_date1;
If li_count1 = 0 Then
li_unit1 := PI_UNITID;
End If;

if li_count1 > 0 Then

--如责任中心中维护个人信息，则取生效时间之前最近生效的一条记录
Select C_DUTYCENTREID
Into li_unit1
From (Select *
From TB_CNB_EMPDUTY
Where C_EMPID = PI_EMPOID
And C_GROUPID = PI_GROUP
And C_EFECTIVETIME <= ls_date1
Order By C_EFECTIVETIME Desc) a
Where rownum = 1;

End If;
--以上获取了员工的成本部门信息li_unit1,接下来要用员工的成本部门去获取员工所在的成本中心
ls_month := '0' || ps_month;
ls_date := ps_year || substr(ls_month, length(ls_month) - 1);

li_id := li_unit1;
--
--如果是责任中心，直接返回
Select Count(*)
Into li_count
From tb_cnb_dutycenter d
Where d.c_unitid = li_id
And d.c_efectivetime <= ls_date;

If li_count > 0 Then
Select a.c_unitid, a.c_compid
Into li_dutycenter, li_orgunit
From (Select *
From TB_CNB_DUTYCENTER DC
Where DC.C_UNITID = li_id
And C_EFECTIVETIME <= ls_date
Order By C_EFECTIVETIME Desc) a
Where rownum = 1;
insert into tb_cnb_dutycenterjudge
values
(PI_EMPOID,
PI_GROUP,
PI_UNITID,
PS_YEAR,
PS_MONTH,
li_dutycenter,
PS_DELIVERNUM);

Return li_dutycenter;

End If;

--先根据员工OID查出其对应的机构，放入li_parentorgunit中作为待查条件
select C_ORGID
into li_parentorgunit
from tb_inf_employee emp
where emp.c_oid = PI_EMPOID;

if li_parentorgunit <> PI_UNITID then

Loop

select count(*)
into li_count1
From tb_org_unitrelation

Where c_orgunitid = li_id
And c_hiberarchyid = 1
And c_status = 1;

if li_count1 = 0 then

insert into tb_cnb_dutycenterjudge
values
(PI_EMPOID,
PI_GROUP,
PI_UNITID,
PS_YEAR,
PS_MONTH,
PI_UNITID,
PS_DELIVERNUM);
Return PI_UNITID;
end if;

Select c_parentunitid
Into li_pid
From tb_org_unitrelation
Where c_orgunitid = li_id
And c_hiberarchyid = 1
And c_status = 1;

Exit When li_pid = li_parentorgunit;

--如果不是责任中心，循环查找直到找到责任中心

--先判断是否是责任中心
Select Count(*)
Into li_count
From tb_cnb_dutycenter d
Where d.c_unitid = li_pid
And d.c_efectivetime <= ls_date;

If li_count > 0 Then

Select a.c_unitid, a.c_compid
Into li_dutycenter, li_orgunit
From (Select *
From TB_CNB_DUTYCENTER DC
Where DC.C_UNITID = li_pid
And C_EFECTIVETIME <= ls_date
Order By C_EFECTIVETIME Desc) a
Where rownum = 1;
Exit;
Else
li_id := li_pid;
End If;

End Loop;

end if;

-- 如果最终没有得出责任中心的值，则把员工所在组织机构赋值给责任中心
if li_dutycenter = 0 Then

li_dutycenter := PI_UNITID;

End if;
insert into tb_cnb_dutycenterjudge
values
(PI_EMPOID,
PI_GROUP,
PI_UNITID,
PS_YEAR,
PS_MONTH,
li_dutycenter,
PS_DELIVERNUM);

Return li_dutycenter;

End GET_EMPCENTER;