Question

我试图选择max（行数）。这是我的两个SELECT

变种

SELECT MAX(COUNT_OF_ENROLEES_BY_SPEC) FROM
(SELECT D.SPECCODE, COUNT(D.ENROLEECODE) AS COUNT_OF_ENROLEES_BY_SPEC
 FROM DECLARER D
 GROUP BY D.SPECCODE
);

SELECT S.NAME, MAX(D.ENROLEECODE)
  FROM SPECIALIZATION S
    CROSS JOIN DECLARER D WHERE S.SPECCODE = D.SPECCODE
  GROUP BY S.NAME
  HAVING MAX(D.ENROLEECODE) = 
  ( SELECT MAX(COUNT_OF_ENROLEES_BY_SPEC) FROM
      ( SELECT D.SPECCODE, COUNT(D.ENROLEECODE) AS COUNT_OF_ENROLEES_BY_SPEC
        FROM DECLARER D
        GROUP BY D.SPECCODE
      )
  );

第一个工作正常，但我想用＃34; HAVING＆＃34;重写它。就像在我的第二个变体中，再添加一列。但现在第二个变量不输出结果中的任何数据，只是空列。我该如何解决？谢谢你！）

Answer 1

此查询基于评论中给出的描述和一些建议，因此可能是错误的：

select                   -- 4. Join selected codes with specializations
  S.Name,
  selected_codes.spec_code,
  selected_codes.count_of_enrolees_by_spec   
from 
  specialization S,
  ( 
    select               -- 3. Filter records with maximum popularity only
      spec_code, 
      count_of_enrolees_by_spec
    from (
      select             -- 2. Count maximum popularity in separate column
        spec_code, 
        count_of_enrolees_by_spec,
        max(count_of_enrolees_by_spec) over (partition by null) max_count
      from (
        SELECT           -- 1. Get list of declarations and count popularity
          D.SPECCODE           AS SPEC_CODE, 
          COUNT(D.ENROLEECODE) AS COUNT_OF_ENROLEES_BY_SPEC
        FROM DECLARER D
        GROUP BY D.SPECCODE
      )
    )
    where count_of_enrolees_by_spec = max_count
  )
    selected_codes
where 
  S.SPECCODE = selected_codes.spec_code

同样查询未经测试，可能会出现一些语法错误。

SQL嵌套聚合函数MAX（COUNT（*））

1 个答案: