利用视图查询效率会变慢?
ptpa 2006-12-26 08:04:58 VIEW_STU_SCHEME 为视图
cj_lncjb ,cj_lrcjb 为表
select a.kch,a.kcm,a.xh,b.stu_sch_group_num,b.stu_sch_group_name
from cj_lncjb a, VIEW_STU_SCHEME b
where b.kch=a.kch and b.xh=a.xh and b.xh='1923206'
union
select a.kch,a.kcm,a.xh,b.stu_sch_group_num,b.stu_sch_group_name
from cj_lrcjb a,VIEW_STU_SCHEME b
where b.kch=a.kch and b.xh=a.xh and a.lrzt='1' and b.xh='1923206'
--这个语句查询时间需要0.06秒
但是 先创建视图:
create or replace view v_allcj as
select kch,kcm,xh from cj_lncjb
union
select kch,kcm,xh from cj_lrcjb where lrzt='1'
然后执行:
select a.kch,a.kcm,a.xh,b.stu_sch_group_num,b.stu_sch_group_name from
v_allcj a,VIEW_STU_SCHEME b where b.kch=a.kch and b.xh=a.xh and b.xh='1923206'
--这个语句执行10分钟都没出结果
请问一下这是为什么?