比较大小函数SIGN
sign(x)或者Sign(x)叫做符号函数，其功能是取某个数的符号（正或负）：当x>0，sign(x)=1;当x=0，sign(x)=0;当x<0， sign(x)=-1；
x可以是函数或计算表达式
有学生成绩表student,现在要用decode函数实现以下几个功能：成绩>85,显示优秀；>70显示良好；>60及格；否则是不及格。
假设student的编号为id,成绩为score,那么：
select id,decode(sign(score-85),1,'优秀',-1,
decode(sign(score-70),'良好',
decode(sign(score-60),'及格','不及格')))
from student；
decode 和 case when 使用原理都是一样的
SELECT
decode( sign(AllPerson.ID_-smallpct.HR_EFF_PPLAN_CYCLE_ID_),
(AllPerson.AllPersonCount-smallpct.smallpctCount),
AllPerson.AllPersonCount) AS noToReportNum
from
( SELECT COUNT( pcpt1.HR_EFF_PPLAN_CYCLE_ID_) smallpctCount,pcpt1.HR_EFF_PPLAN_CYCLE_ID_ FROM
HR_EFF_PPLAN_CYCLE cycle1,hr_eff_plan ep1,HR_EFF_PFMCE_PLAN pp1,
HR_EFF_PFMCE_PLANEECPT pcpt1
WHERE
ep1.STATUS_='0' AND cycle1.STATUS_='0' AND pp1.STATUS_='0' AND pcpt1.STATUS_='0'
AND pcpt1.HR_EFF_PFMCE_PLAN_ID_=pp1.ID_
AND pcpt1.HR_EFF_PPLAN_CYCLE_ID_=cycle1.ID_
and to_char(sysdate,'yy-MM')>=to_char(cycle1.OBJ_REPORT_STIME_,'yy-MM')
AND cycle1.HR_EFF_PFMCE_PLAN_ID_=pp1.ID_
AND pp1.HR_EFF_PLAN_ID_=ep1.ID_ GROUP BY pcpt1.HR_EFF_PPLAN_CYCLE_ID_ ) smallpct
,
( SELECT COUNT(news1.ID_) AllPersonCount,cycle1.ID_ FROM
HR_EFF_PPLAN_CYCLE cycle1,hr_eff_news news1,HR_EFF_PFMCE_PLAN pp1
WHERE
ep1.STATUS_='0' AND cycle1.STATUS_='0' AND pp1.STATUS_='0'
and to_char(sysdate,'yy-MM')
AND cycle1.HR_EFF_PFMCE_PLAN_ID_=pp1.ID_
AND pp1.HR_EFF_PLAN_ID_=ep1.ID_
AND news1.HR_EFF_PLAN_ID_=ep1.ID_ GROUP BY cycle1.ID_ ) AllPerson
SELECT decode ( (COUNT(1)),2,(COUNT(1)) ) from ( SELECT COUNT( pcpt1.HR_EFF_PPLAN_CYCLE_ID_) smallpctCount,pcpt1.HR_EFF_PPLAN_CYCLE_ID_ FROM HR_EFF_PPLAN_CYCLE cycle1,HR_EFF_PFMCE_PLANEECPT pcpt1 WHERE ep1.STATUS_='0' AND cycle1.STATUS_='0' AND pp1.STATUS_='0' AND pcpt1.STATUS_='0' AND pcpt1.HR_EFF_PFMCE_PLAN_ID_=pp1.ID_ AND pcpt1.HR_EFF_PPLAN_CYCLE_ID_=cycle1.ID_ and to_char(sysdate,'yy-MM') AND cycle1.HR_EFF_PFMCE_PLAN_ID_=pp1.ID_ AND pp1.HR_EFF_PLAN_ID_=ep1.ID_ GROUP BY pcpt1.HR_EFF_PPLAN_CYCLE_ID_ ) hasReport
