Oracle的数据库对象分为五种：表，视图，序列，索引和同义词。
一、视图
视图是基于一个表或多个表或视图的逻辑表，本身不包含数据，通过它可以对表里面的数据进行查询和修改。视图基于的表称为基表。
视图的优点：
1.对数据库的访问，因为视图可以有选择性的选取数据库里的一部分。
2.用户通过简单的查询可以从复杂查询中得到结果。
3.维护数据的独立性，试图可从多个表检索数据。
4.对于相同的数据可产生不同的视图。 视图分为简单视图和复杂视图：
简单视图只从单表里获取数据
复杂视图从多表
创建视图
CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view_name
[(alias[, alias]...)]
AS subquery
[WITH CHECK OPTION [CONSTRAINT constraint]]
[WITH READ ONLY]
其中：
OR REPLACE ：若所创建的试图已经存在，ORACLE自动重建该视图；
FORCE ：不管基表是否存在ORACLE都会自动创建该视图；
NOFORCE ：只有基表都存在ORACLE才会创建该视图：
alias ：为视图产生的列定义的别名；
subquery ：一条完整的SELECT语句，可以在该语句中定义别名；
WITH CHECK OPTION ：
插入或修改的数据行必须满足视图定义的约束；
WITH READ ONLY ：
该视图上不能进行任何DML操作。
---------------------
二、视图使用
生成视图并且产生一个新的合计行
create or replace view v_wjx_hz as
select "TERRITORIALITYUNIT","YEAR","MONTH","WORKID","DEVICE_ID","DEVICE_NAME","DEVICE_LOCNO","DEV_CLASS_ID","DEVICE_PRESSURE_LEVEL","T_JXZS","T_JTDX","T_ZXXX","T_TS","T_GHFT","T_GHPM","T_FKD","T_OXH","T_ZHQPT","G_JXZS","G_KG","G_PW","G_Z","G_BZ","G_GHLXS","G_GHOXH","F_FMWH","F_FMBWH","F_CLWH","F_CLBWH","F_QNJZQXY","F_QNJZRHY","F_QNJZMFZ" from
(
select t1.territorialityunit,
t1.year,
t1.month,
t1.workid,
t1.device_id,
t1.device_name,
t1.device_locno,
t1.dev_class_id,
t1.device_pressure_level,
t2.t_jxzs,
t2.t_jtdx,
t2.t_zxxx,
t2.t_ts,
t2.t_ghft,
t2.t_ghpm,
t2.t_fkd,
t2.t_oxh,
t2.t_zhqpt,
t3.g_jxzs,
t3.g_kg,
t3.g_pw,
t3.g_z,
t3.g_bz,
t3.g_ghlxs,
t3.g_ghoxh,
t4.f_fmwh,
t4.f_fmbwh,
t4.f_clwh,
t4.f_clbwh,
t4.f_qnjzqxy,
t4.f_qnjzrhy,
t4.f_qnjzmfz
from eam_wjx_result_tb t1
left join (select decode(t_jtdx,null,0,t_jtdx)+decode(t_zxxx,null,0,t_zxxx)+decode(t_ts,null,0,t_ts) as t_jxzs, t5.* from (select workid,
sum(case jxfs
when '1' then
1
end) as t_jtdx,
sum(case jxfs
when '2' then
1
end) as t_zxxx,
sum(case jxfs
when '3' then
1
end) as t_ts,
sum(ghft) as t_ghft,
sum(ghpm) as t_ghpm,
sum(fkd) as t_fkd,
sum(oxh) as t_oxh,
sum(zhqpt) as t_zhqpt
from eam_wjx_result_tyq_tb
group by workid) t5) t2
on t1.workid = t2.workid
left join (select decode(g_kg,null,0,g_kg)+decode(g_pw,null,0,g_pw) as g_jxzs, t6.* from (select workid,
sum(case jxfs
when '1' then
1
end) as g_kg,
sum(case jxfs
when '2' then
1
end) as g_pw,
sum(case lxsfz
when '3' then
1
end) as g_z,
sum(case lxsfz
when '4' then
1
end) as g_bz,
sum(ghlxs) as g_ghlxs,
sum(ghoxh) as g_ghoxh
from eam_wjx_result_glq_tb
group by workid) t6) t3
on t1.workid = t3.workid
left join (select workid,
sum(case fmsfwh
when '1' then
1
end) as f_fmwh,
sum(case fmsfwh
when '0' then
1
end) as f_fmbwh,
sum(case clxsfwh
when '1' then
1
end) as f_clwh,
sum(case clxsfwh
when '0' then
1
end) as f_clbwh,
sum(qnjzqxy) as f_qnjzqxy,
sum(qnjzrhy) as f_qnjzrhy,
sum(qnjzmfz) as f_qnjzmfz
from eam_wjx_result_fm_tb
group by workid) t4
on t1.workid = t4.workid
union all
select '合计' territorialityunit,
null year,
month,
null workid,
null device_id,
null device_name,
null device_locno,
null dev_class_id,
null device_pressure_level,
sum(t2.t_jxzs),
sum(t2.t_jtdx),
sum(t2.t_zxxx),
sum(t2.t_ts),
sum(t2.t_ghft),
sum( t2.t_ghpm),
sum(t2.t_fkd),
sum(t2.t_oxh),
sum( t2.t_zhqpt),
sum( t3.g_jxzs),
sum( t3.g_kg),
...三、生成唯一的编号
有时候业务需要一些关联字段，而这些关联字段是不能随意改变的。所以就要生成唯一的编号了。
生成唯一的编号要确保编号构成的每个元素都是唯一的，比如通过主键，种类或类型以及其他固定不变来拼成编号
具体使用
判断相同来避免生成重复的编号
select ml.*,(ml.MAINTAIN_ID||ml.MAINTAIN_TYPE||ml.MAINTAIN_ID||ml.MAINTAIN_UNIT||ml.MAINTAIN_ID) as ORANDID from (select * from(select * from(select '1' as MAINTAIN_TYPE,m.* from(select distinct(mm.MAINTAIN_NAME) as MAINTAIN_NAME,mm.MAINTAIN_UNIT,mm.MAINTAIN_LEVEL,mm.MAINTAIN_MONTH,(select max(ll.WELLPLAN_ID) from MAINTAIN_WELL_PLAN ll where ll.well_name = mm.MAINTAIN_NAME and ll.manage_unit = mm.MAINTAIN_UNIT and ll.pressure_level = mm.MAINTAIN_LEVEL and ll.plan_month = mm.MAINTAIN_MONTH) as MAINTAIN_ID from (select distinct(t.well_name) as MAINTAIN_NAME,t.manage_unit as MAINTAIN_UNIT,t.pressure_level as MAINTAIN_LEVEL,t.plan_month as MAINTAIN_MONTH,t.WELLPLAN_ID as MAINTAIN_ID from MAINTAIN_WELL_PLAN t) mm)m) order by MAINTAIN_MONTH desc)
union all
select * from(select * from(select '2' as MAINTAIN_TYPE,m.* from(select distinct(mm.MAINTAIN_NAME) as MAINTAIN_NAME,mm.MAINTAIN_UNIT,mm.MAINTAIN_LEVEL,mm.MAINTAIN_MONTH,(select max(ll.VOLTAGEPLAN_ID) from MAINTAIN_VOLTAGE_PLAN ll where ll.voltage_name = mm.MAINTAIN_NAME and ll.manage_unit = mm.MAINTAIN_UNIT and ll.pressure_level = mm.MAINTAIN_LEVEL and ll.plan_month = mm.MAINTAIN_MONTH) as MAINTAIN_ID from (select distinct(t.voltage_name) as MAINTAIN_NAME,t.manage_unit as MAINTAIN_UNIT,t.pressure_level as MAINTAIN_LEVEL,t.plan_month as MAINTAIN_MONTH,t.VOLTAGEPLAN_ID as MAINTAIN_ID from MAINTAIN_VOLTAGE_PLAN t) mm) m) order by MAINTAIN_MONTH desc)
union all
select * from(select * from(select '3' as MAINTAIN_TYPE,m.* from(select distinct(mm.MAINTAIN_NAME) as MAINTAIN_NAME,mm.MAINTAIN_UNIT,mm.MAINTAIN_LEVEL,mm.MAINTAIN_MONTH,(select max(ll.MIDLOW_ID) from MAINTAIN_MIDLOW_PLAN ll where ll.midlow_name = mm.MAINTAIN_NAME and ll.manage_unit = mm.MAINTAIN_UNIT and ll.plan_month = mm.MAINTAIN_MONTH) as MAINTAIN_ID from (select distinct(t.midlow_name) as MAINTAIN_NAME,t.manage_unit as MAINTAIN_UNIT,t.pressure_level as MAINTAIN_LEVEL,t.plan_month as MAINTAIN_MONTH,t.MIDLOW_ID as MAINTAIN_ID from MAINTAIN_MIDLOW_PLAN t)mm)m) order by MAINTAIN_MONTH desc)) ml