Question

以下查询在包含2个字段的表上执行：BEGDATE和AMOUNT（均为varchar2）。目的是显示如下数据：

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

这个想法是根据年份和学期计算字段数量的总和。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))才能达到预期的效果？

 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

Answer 1

只需在选择列列表的末尾添加一个总和即可。

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，当你正在分组时，你不再需要它了。

Answer 2

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;

案例陈述中的SUM函数

2 个答案: