MAX函数和GROUP BY函数不能一起工作

Question

我想列举教授“java”的姓名教授，他教的次数以及他教授的最新年份和学期。

我试过这个查询，但它给了两个同名的行。

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 

代码，错误：

我还试图吨他的代码与条件 “AND f.CO_YEAR = MAX（f.CO_YEAR）”，但它显示这个错误 “功能组这里不允许”

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 

---

修订

---

此代码显示最近一年的输出，但问题是当它提取最新的行时，计数器停在那里并显示1个值。但我想统计所有的行，然后只显示最新的一年。

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 

新的输出：

1 Gaurav 1 4 2006 

预期输出：

1 Gaurav 2 4 2006 

Answer 1

这个查询，我还没有尝试过什么，但：

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

试试这个（我没有测试它）

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