SQL 错误 : ORA-00932: inconsistent datatypes: expected CHAR got NUMBER

Question

每次它给我一个空结果时，我都试图得到一个结果“无”。现在它给我一个 0 的空结果。对于空结果，我怎么能有一行显示“无”而不是 0。

我已尝试使用 TO_CHAR 和 TO_NUMBER 作为总和，但无法显示“无”...

CASE WHEN SUM(ENROLLED) = 0 THEN 'none' ELSE SUM(ENROLLED) END AS ENROLLED

所以当尝试上述操作时，我得到 SQL 错误:ORA-00932:不一致的数据类型:预期的 CHAR 得到了 NUMBER

这就是我所拥有的

SELECT lt.STUDENT_ID,lt.FIRST_NAME, lt.LAST_NAME, CASE WHEN SUM(ENROLLED) = 0 THEN 'none' ELSE SUM(ENROLLED) END AS ENROLLED
FROM STUDENT lt
LEFT OUTER JOIN
(SELECT s.STUDENT_ID, e.ENROLL_DATE,COUNT(z.COURSE_NO)AS ENROLLED
FROM   STUDENT s
LEFT   JOIN ENROLLMENT e ON s.STUDENT_ID = e.STUDENT_ID
LEFT   JOIN SECTION z ON e.SECTION_ID = z.SECTION_ID
WHERE  s.PHONE LIKE '702%'
GROUP  BY s.STUDENT_ID, e.ENROLL_DATE) rt
ON lt.STUDENT_ID = rt.STUDENT_ID
WHERE lt.PHONE LIKE '702%'
GROUP BY lt.STUDENT_ID,lt.FIRST_NAME, lt.LAST_NAME,ENROLLMENTS;

而不是拥有

STUDENT_ID FIRST_NAME                LAST_NAME                 ENROLLED
---------- ------------------------- ------------------------- -----------
       253 Walter                    Boremmann                     1 
       396 James E.                  Norman                        0 
etc

我想要这样的

STUDENT_ID FIRST_NAME                LAST_NAME                 ENROLLED
---------- ------------------------- ------------------------- -----------
       253 Walter                    Boremmann                     1 
       396 James E.                  Norman                        none

Answer 1

尝试使用函数:COALESCE (cast(sum(expr1) as varchar), 'none')

作为旁注，我质疑您在查询中使用 DISTINCT。