Question

我想列出教授“java”的名字教授，他教过的次数以及他教的最新年份和学期。

我尝试了这个查询，但它提供了两行同名。

SELECT i.I_FNAME, COUNT(f.I_ID) as myCount, f.CO_TERMNUMBER, f.CO_YEAR
FROM 
  INSTRUCTOR i
JOIN TEACHINGQUALIFICATION t
  ON i.I_ID = t.I_ID
JOIN COURSE c
  ON c.C_ID = t.C_ID
JOIN COURSEOFFERING f
  ON i.I_ID = f.I_ID  
WHERE c.C_TITLE =  'java'
  GROUP BY t.I_ID, i.I_FNAME, f.CO_TERMNUMBER, f.CO_YEAR
  ORDER BY f.CO_YEAR desc

输出：

1    Gaurav    1    4   2006
2    Gaurav    1    1   2000

预期输出：

1    Gaurav    2    4   2006

错误代码：

我也尝试使用条件“AND f.CO_YEAR = MAX（f.CO_YEAR）”但是它显示此错误“此处不允许组功能”

SELECT  t.I_ID, i.I_FNAME, COUNT(f.I_ID) as Cnt, f.CO_TERMNUMBER, f.CO_YEAR
FROM 
  INSTRUCTOR i
JOIN TEACHINGQUALIFICATION t
  ON i.I_ID = t.I_ID
JOIN COURSE c
  ON c.C_ID = t.C_ID
JOIN COURSEOFFERING f
  ON i.I_ID = f.I_ID  
WHERE c.C_TITLE =  'itec801' AND f.CO_YEAR= MAX (f.CO_YEAR)
  GROUP BY t.I_ID, i.I_FNAME, f.CO_TERMNUMBER, f.CO_YEAR
  ORDER BY f.CO_YEAR desc

已更新

此代码显示的是最近一年的输出，但问题是它何时获取最新行，计数器停在那里并显示1值。但我想计算所有行，然后只显示最新一年。

SELECT  t.I_ID, i.I_FNAME, COUNT(f.I_ID) as Cnt, f.CO_TERMNUMBER, f.CO_YEAR
    FROM 
      INSTRUCTOR i
    JOIN TEACHINGQUALIFICATION t
      ON i.I_ID = t.I_ID
    JOIN COURSE c
      ON c.C_ID = t.C_ID
    JOIN COURSEOFFERING f
      ON i.I_ID = f.I_ID  
 JOIN
    (
    SELECT I_ID, MAX(CO_YEAR) LatestYear
    FROM COURSEOFFERING GROUP BY I_ID
    ) 
  f2 ON f.I_ID = f2.I_ID AND f.CO_YEAR = f2.LatestYear

    WHERE c.C_TITLE =  'itec801' 
      GROUP BY t.I_ID, i.I_FNAME, f.CO_TERMNUMBER, f.CO_YEAR
     having  f.CO_YEAR= MAX (f.CO_YEAR)
      ORDER BY f.CO_YEAR desc

新输出：

1    Gaurav    1    4   2006

预期输出：

1    Gaurav    2    4   2006

Answer 1

这个查询怎么样，我还没试过，但是：

SELECT  i.I_FNAME, COUNT(f.I_ID) as Cnt, MAX(f.CO_TERMNUMBER), MAX(f.CO_YEAR)
FROM 
  INSTRUCTOR i
JOIN TEACHINGQUALIFICATION t
  ON i.I_ID = t.I_ID
JOIN COURSE c
  ON c.C_ID = t.C_ID
JOIN COURSEOFFERING f
  ON i.I_ID = f.I_ID
WHERE c.C_TITLE =  'itec801'
  GROUP BY i.I_FNAME

Answer 2

   If you have aggeragate function then use having statement like and must below  order :
     select * from table
     where cond...
     group by ...
     having cond ...
     order by..
    =======================
    Exapmle:

      SELECT  t.I_ID, i.I_FNAME, COUNT(f.I_ID) as Cnt, f.CO_TERMNUMBER, f.CO_YEAR
        FROM 
       INSTRUCTOR i
       left outer JOIN TEACHINGQUALIFICATION t  ON i.I_ID = t.I_ID
       left outer JOIN COURSE c  ON c.C_ID = t.C_ID
       left outer JOIN COURSEOFFERING f  ON i.I_ID = f.I_ID  
       WHERE c.C_TITLE =  'itec801' 
       GROUP BY t.I_ID, i.I_FNAME, f.CO_TERMNUMBER, f.CO_YEAR
       having  f.CO_YEAR= MAX (f.CO_YEAR)
       ORDER BY f.CO_YEAR desc

Answer 3

您需要使用Having clause

尝试这个（我没有测试过）

SELECT  t.I_ID, i.I_FNAME, COUNT(f.I_ID) as Cnt, f.CO_TERMNUMBER, f.CO_YEAR
FROM 
  INSTRUCTOR i
JOIN TEACHINGQUALIFICATION t
  ON i.I_ID = t.I_ID
JOIN COURSE c
  ON c.C_ID = t.C_ID
JOIN COURSEOFFERING f
  ON i.I_ID = f.I_ID  
WHERE c.C_TITLE =  'itec801'
  GROUP BY t.I_ID, i.I_FNAME, f.CO_TERMNUMBER, f.CO_YEAR
  HAVING f.CO_YEAR= MAX (f.CO_YEAR)
  ORDER BY f.CO_YEAR desc

MAX功能和GROUP BY功能不能一起工作

3 个答案: