Oracle SQL 优化全过程

前两天写了一个课程结束时间的统计，要求是有课程所在院系、学生所在院系、课程相关信息以及课程结束时间等信息，其中课程结束时间是以星期做单位，没有太多思考，我很简单地写出了查询的SQL，但是执行效率太低,现将整个SQL的优化过程称述如下:

 

优化前:

 

视图一：

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sql 代码

CREATE OR REPLACE VIEW V_A_WEIXM_SUB_BAD
(TEACHINGCLASSID, TEACHINGCLASSNAME, TERMID, COURSENAME, COURSENO,
 TOTALPERIODNUM, CLASSNO, TERMNAME, DKNAME, STNAME,
 DSNAME, NUM, TEACHER1, TEACHER2, TEACHER3,
 BEGINWEEK, REST, WEEKDAY)
AS
select
    distinct a.teachingclassid,a.teachingclassname,a.termid,b.coursename,b.COURSENO,b.TOTALPERIODNUM,
    c.CLASSNO,l.TERMNAME,e.name dkname,h.NAME stname,j.NAME dsname,
    g.num,k.TEACHER1,k.TEACHER2,k.TEACHER3,a.BEGINWEEK,
    (select max(weekno) from caresult where caresult.teachingclassid=a.teachingclassid ) rest,
    decode(
 (
 select weekdayno from
 (
     select distinct max(s.weekdayno) weekdayno,s.teachingclassid from
     (
         select distinct max(weekno) weekno,teachingclassid from caresult group by teachingclassid
     ) m,caresult s
     where m.teachingclassid=s.teachingclassid and m.weekno=s.weekno group by s.teachingclassid
 ) where teachingclassid=a.teachingclassid
 )
  ,1,'星期一',2,'星期二',3,'星期三',4,'星期四',5,'星期五',6,'星期六',0,'星期日') WEEKDAY
from
    teachingtask a,course b,course_classes c,
    (select distinct classno,count(classno) num from students group by classno)g,
    staffroom h,classes i,
    TEACHERSETTING k,term l,department j,department e
where
    a.courseid=b.courseid and a.teachingclassid=c.teachingclassid and
    b.departmentid=e.departmentid and b.STAFFROOMID=h.STAFFROOMID and
    c.CLASSNO=i.CLASSNO and i.DEPARTMENTID=j.DEPARTMENTID and
    g.CLASSNO=c.CLASSNO and k.teachingclassid(+)=a.teachingclassid and
    a.TERMID=l.TERMID
    and a.TERMID='t012' order by e.name,h.NAME,b.COURSENO,b.coursename,teachingclassname;

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优化后:

 

视图二：

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sql 代码

CREATE OR REPLACE VIEW V_A_WEIXM_SUB
(TEACHINGCLASSID, TEACHINGCLASSNAME, TERMID, COURSENAME, COURSENO,
 TOTALPERIODNUM, CLASSNO, TERMNAME, DKNAME, STNAME,
 DSNAME, NUM, TEACHER1, TEACHER2, TEACHER3,
 BEGINWEEK, REST, WEEKDAY)
AS
select
    distinct a.teachingclassid,a.teachingclassname,a.termid,b.coursename,b.COURSENO,b.TOTALPERIODNUM,
    c.CLASSNO,l.TERMNAME,e.name dkname,h.NAME stname,j.NAME dsname,
    g.num,k.TEACHER1,k.TEACHER2,k.TEACHER3,a.BEGINWEEK,
    m.weekno rest,
    decode(m.weekdayno,1,'星期一',2,'星期二',3,'星期三',4,'星期四',5,'星期五',6,'星期六',0,'星期日') WEEKDAY
from
    teachingtask a,course b,course_classes c,
    (select distinct classno,count(classno) num from students group by classno)g,
    staffroom h,classes i,
    (
        select
            a.weekdayno,a.weekno,b.teachingclassid,a.trueflag from
            (select weekdayno,weekno,teachingclassid,(to_number(weekno)*10+to_number(weekdayno)) trueflag from caresult) a,
            (select teachingclassid,max(to_number(weekno)*10+to_number(weekdayno)) checkflag from caresult group by teachingclassid)b
        where b.teachingclassid=a.teachingclassid and b.checkflag=a.trueflag
    ) m,
    TEACHERSETTING k,term l,department j,department e
where
    a.courseid=b.courseid and a.teachingclassid=c.teachingclassid and
    b.departmentid=e.departmentid and b.STAFFROOMID=h.STAFFROOMID and
    c.CLASSNO=i.CLASSNO and i.DEPARTMENTID=j.DEPARTMENTID and
    g.CLASSNO=c.CLASSNO and k.teachingclassid(+)=a.teachingclassid and
    a.TERMID=l.TERMID  and m.teachingclassid(+)=a.teachingclassid
    and a.TERMID='t012' order by e.name,h.NAME,b.COURSENO,b.coursename,teachingclassname;

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