sql - oracle SQL.merge 多列

Question

我有如下数据

 A     B     
 =     1    
 =     2    
 !=    3    
 =     4    
 !=    5

我需要将这些放入一个列中，以便所有 '!=' 都低于“=”数据，并且只有在列 A 中存在带有 '!=' 的行时，才将 '!=' 作为虚拟行

   1
   2
   4
   !=
   3
   5

Answer 1

用于union all获取行中所需的所有值。添加一列以指定展示位置。该列的顺序：

select value
from (select cast(B as varchar2(255)) as value, 1 as which
      from t
      where A <> '!='
      union all
      select '!=', 2 from dual
      union all
      select cast(B as varchar2(255)) , 3
      from t
      where A = '!='
    ) s
order by which;

编辑：

对于修订版：

select value
from ((select cast(B as varchar2(255)) as value, 1 as which
       from t
       where A <> '!='
      ) union all
      (select '!=', 2 from dual where exists (select 1 from t where A = '!=')
      ) union all
      (select cast(B as varchar2(255)), 3
       from t
       where A = '!='
      )
    ) s
order by which;