sql 占位符行

Question

我有一个顶点项 P_USERS，它的值可以高于从下面的查询返回的行数。

我有一份经典报告，其中包含以下查询：

  select 
       first_name,
       last_name
  from  accounts
  where account_role = 'Author'
  order by account_nr;

如果查询中的总行数小于 apex_item 中的值，我希望将占位符行添加到查询中（first_name = null、last_name = null 等） P_USERS.

关于如何实现这一目标的任何提示？也许用 LEFT join?

Answer 1

您可以尝试使用 LEFT JOIN。

首先，创建一个数字列表，直到达到您想要的限制，例如 suggested here：

-- let's say you want 300 records
Select Rownum r From dual Connect By Rownum <= 300

然后你可以使用它来左连接并有空记录：

SELECT C, R FROM  
  ( select rownum i, c from (select  'a' c from dual union all select 'b' from dual) )
, ( Select Rownum r From dual Connect By Rownum <= 300)
where i(+)= r order by r

以上为您提供了一个有序列表，从 'a'、'b' 开始，然后是 null 直到结束。

所以你可以根据你的情况调整它：

SELECT F,L FROM  
  ( select rownum i, f, l from (
             select first_name f, last_name l 
               from  accounts where account_role = 'Author'
            order by account_nr) )
, ( Select Rownum r From dual Connect By Rownum <= 300)
where i(+)= r

Answer 2

如果您的结果多于您定义的最小值，则必须将其余部分与并集相加。

以下是您可以根据自己的情况尝试调整的内容：

  SELECT i,c FROM  (
select rownum i, c from (
select  'a' c from dual union all select 'b' from dual union all select 'd' from dual union all select 'be' from dual
)), (Select Rownum r From dual Connect By Rownum <= 3)
where (i(+)= r)
union select i,c from (select rownum i, c from (
select  'a' c from dual union all select 'b' from dual union all select 'd' from dual union all select 'be' from dual
)) where i>3

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