按别名分组(Oracle)

Question

如何使用别名"分组"查询,例如:

select count(*), (select * from....) as alias_column 
from table 
group by alias_column

我得到'alias_column':INVALID_IDENTIFIER错误消息.为什么？如何分组此查询？

Answer 1

select
  count(count_col),
  alias_column
from
  (
  select 
    count_col, 
    (select value from....) as alias_column 
  from 
    table
  ) as inline
group by 
  alias_column

如果在GROUP BY子句中重复相应的表达式,则分组通常有效.只提一个别名是不可能的,因为SELECT步骤是执行查询的最后一步,分组发生在早期,当别名尚未定义时.

对于GROUP BY子查询的结果,您将需要稍微绕道并使用嵌套查询,如上所示.

Answer 2

使用别名列嵌套查询:

select count(*), alias_column
from
( select empno, (select deptno from emp where emp.empno = e.empno) as alias_column
  from emp e
)
group by alias_column;