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。
我已经尝试过 NVL(SUM(ENROLLED),'none') AS ENROLLED 并且它不起作用
SELECT DISTINCT lt.STUDENT_ID,lt.FIRST_NAME, lt.LAST_NAME, NVL(SUM(ENROLLED),'none') 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;
现在我得到
STUDENT_ID FIRST_NAME LAST_NAME ENROLLED
---------- ------------------------- ------------------------- -----------
253 Walter Boremmann 1
396 James E. Norman 0
etc
但我想要
STUDENT_ID FIRST_NAME LAST_NAME ENROLLED
---------- ------------------------- ------------------------- -----------
253 Walter Boremmann 1
396 James E. Norman none