oracle3

Posted 2020-09-27

--创建视图
create[or replace]
    [force|--不管基表是否存在都创建视图。
    noforce]--仅当基表存在时才创建视图（默认）。
    view view
    [(alias[,alias]…)]
    as subquery--子查询，决定了视图对应的数据。
    [with check option[constraint constraint]]--指明对视图操作时，必须满足子查询中的约束条件。
    [with read only[constraint constraint]];--指明该视图为只读视图，不能修改。
--创建TOP-N视图
--内嵌视图有一种特殊的应用，称为Top-N-Analysis查询，通过使用伪列ROWNUM，为查询结果集排序，并返回符合条件的记录。
select[column_list],rownum
    from(select[column_list]from table order by top-n_column)
    where rownum＜=n;
--例1
select * from 
(
    select employee_id,first_name,last_name,salary from employee order by salary desc
)nested_order where rownum <= 5;--查询工资排在前1~5名的员工号，员工名，工资，及其工资排号。
--例2
select * from t_test4     where rownum <= 5;--也是可以的

--例3
select * from 
(
   select rownum num,employee_id,first_name,last_name,salary from 
                                                                (
                                                                    select employee_id,first_name,last_name,salary from employee order by salary desc 
      ·                                                            )nested_order1 
)nested_order2    where num between 5 and 10;--查询工资排在前5~10名的员工号，员工名，工资，及其工资排号。
--那么问题来了，为什么内嵌查询可以rownum>1
--分页查询
--第一种方式 
select * from
(
    select a.*, rownum as rn from css_bl_view a    where capture_phone_num = ‘(1) 925-4604800‘
)b where b.rn between 6 and 10;
    
--第二种方式 
select * from css_bl_view a
    where capture_phone_num = ‘(1) 925-4604800‘ and rownum <= 10
    minus
select * from css_bl_view a
    where capture_phone_num = ‘(1) 925-4604800‘ and rownum <= 5;
        
--第三种方式
select * from
(
    select a.*, rownum as rn from css_bl_view a    where capture_phone_num = ‘(1) 925-4604800‘    and rownum <= 10
)b where b.rn > 5;
--一个用rownum的小技巧
select decode(rownum-min_sno,0,a.owner,null) owner,decode(rownum-min_sno,0,1,rownum+1-min_sno) sno, a.name
    from (select *    from t_test8 order by owner, name ) a,
         (select owner, min(rownum) min_sno    from( select *    from t_test8 order by owner, name)    group by owner) b
    where a.owner=b.owner;