Sql case语句中的SUM函数

下面的查询是在一个包含两个字段的表上执行的：BEGDATE和AMOUNT（都是varchar2）。 目的是按如下方式显示数据：

 Year  Semester Total
 2017   Sem1     545
 2017   Sem2     9877
 2020   Sem1     444

其想法是根据学年和学期计算字段总数。 以下查询能够返回以下内容：

 Year  Semester 
 2017   Sem1     
 2017   Sem2     
 2020   Sem1     

我应该在哪里使用

SUM（TO_NUMBER（AMOUNT））

才能获得期望的结果

 SELECT DISTINCT(SUBSTR (BEGDATE, 1, 4)) AS YEAR,
       CASE
          WHEN SUBSTR (BEGDATE, 5, 2) BETWEEN 1 AND 3
             THEN 'SEM1'
          WHEN SUBSTR (BEGDATE, 5, 2)  BETWEEN 4 AND 6
             THEN 'SEM2'
          WHEN SUBSTR (BEGDATE, 5, 2)  BETWEEN 7 AND 9
             THEN 'SEM3'
          ELSE 'SEM4'
       END SEMESTER
  FROM EMP 
  ORDER BY YEAR DESC,SEMESTER

---

只需在选择列列表的末尾添加一个和即可

SELECT   SUBSTR (begdate, 1, 4) AS YEAR,
         CASE
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 1 AND 3
               THEN 'SEM1'
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 4 AND 6
               THEN 'SEM2'
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 7 AND 9
               THEN 'SEM3'
            ELSE 'SEM4'
         END semester,
         SUM (TO_NUMBER (amount)) sum_val
    FROM emp
GROUP BY SUBSTR (begdate, 1, 4),
         CASE
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 1 AND 3
               THEN 'SEM1'
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 4 AND 6
               THEN 'SEM2'
            WHEN SUBSTR (begdate, 5, 2) BETWEEN 7 AND 9
               THEN 'SEM3'
            ELSE 'SEM4'
         END
ORDER BY YEAR DESC, semester;

此外，在进行分组时，您不再需要使用不同的属性。

添加了

SUM

SELECT A.YEAR,A.SEMESTER, SUM(TO_NUMBER(A.AMOUNT)) AS SUM_AMT
FROM
 (SELECT DISTINCT(SUBSTR (BEGDATE, 1, 4)) AS YEAR,
       CASE
          WHEN SUBSTR (BEGDATE, 5, 2) BETWEEN 1 AND 3
             THEN 'SEM1'
          WHEN SUBSTR (BEGDATE, 5, 2)  BETWEEN 4 AND 6
             THEN 'SEM2'
          WHEN SUBSTR (BEGDATE, 5, 2)  BETWEEN 7 AND 9
             THEN 'SEM3'
          ELSE 'SEM4'
       END SEMESTER,
AMOUNT
  FROM EMP 
  ORDER BY YEAR DESC,SEMESTER)A
GROUP BY YEAR,SEMESTER
ORDER BY YEAR DESC, SEMESTER;

---

应该使用适当的数据类型，如果要存储日期，请使用

日期（时间）

数据类型，如果要存储数字，请使用数字数据类型。这就是他们在那里的目的！您可以添加为另一个选定属性的总和，别忘了按分组。我们是要在线教授JDOE，还是他参加了基本的SQL开发课程？是的，这就是SO的所有问题，以及类似游戏化网站（expertsexchange）的其他帮助。我给你5英镑让你帮我做作业