Question

我需要运行如下查询，但无法识别SHOWNDATE。为什么会这样？

查询已简化为清楚：

select  PYNAME,
        SHOWNDATE=(SELECT MAX(OUTCOMETIME) FROM A where A.ID=B.ID),
        count(PYSUBJECTID)
from B
group by PYNAME,
         SHOWNDATE

Answer 1

我认为On Select子句写成AS SHOWNDATE SHOWNDATE =不正确。

select
PYNAME,
(SELECT MAX(OUTCOMETIME) FROM A where A.ID=B.ID) AS SHOWNDATE,
count(PYSUBJECTID)
from B
group by PYNAME,SHOWNDATE

Answer 2

下面是一个基于Scott模式的示例，该示例演示了如何执行此操作：

SQL> select b.deptno,
  2         (select max(a.sal) from emp a where b.deptno = a.deptno) as showsal,
  3         count(b.empno)
  4  from emp b
  5  group by b.deptno;

    DEPTNO    SHOWSAL COUNT(B.EMPNO)
---------- ---------- --------------
        30       2850              6
        20       3000              3
        10       5000              3

SQL>

或者，应用于您的查询：

select  b.pyname,
        (select max(a.outcometime) from a where a.id = b.id) showndate,
        count(b.pysubjectid)
from b
group by b.pyname;

别忘了将表别名应用于所有列！

Answer 3

ALIAS（在这种情况下为SHOWNDATE）不是有效的标识符，但用于子查询的结果集。别名用于方便起见...没人希望“从A.ID = B.ID的A中选择MAX（OUTCOMETIME）作为列名。”

select 
PYNAME
,SHOWNDATE
,COUNT
from (
select   PYNAME
    ,(SELECT MAX(OUTCOMETIME) FROM A where A.ID=B.ID) SHOWNDATE
    ,count(PYSUBJECTID) COUNT
from B
 Group by PYNAME
)
group by  PYNAME
     ,SHOWNDATE
     ,COUNT

SQL无法使用分组依据中的子查询返回的列

3 个答案: