Question

我有一个查询，其中一个课程（C1，C5，C9 ......等）应该显示状态为DONE/NOT DONE/PENDING的用户的帐户作为结果。请注意，课程可以是DONE/NOT DONE或PENDING：

count(u.userid)   ll.law_name   ll.law_course   ll.law_lesson   ll.score   ll.status
 4                  Berlyin         C1            L1              6.05      Done
 8                  Berlyin         C1            L1              NULL     Not Done

 4                  Elance          C9            L6               3.4      Done
 7                  Elance          C9            L6              NULL     Not Done

 2                  Indix           C5            L12              5.5     Done
 3                  Indix           C10           L3              NULL    Not Done

SELECT count(DISTINCT(u.userid)), ll.law_name, ll.law_course, ll.law_lesson, 
CASE WHEN ll.score >=0 THEN Done
     WHEN ll.score <0 THEN Not Done
     WHEN ll.score !=0 THEN pending END AS "status"
FROM 
users u JOIN law_courses ll ON u.id = ll.userid GROUP BY ll.law_lesson

Answer 1

基本思路是将case语句放在group by中。你对这三个群体的逻辑没有意义（或者至少，＆＃34;未决＆＃34;群体不存在）。但这可能会让你走上正轨：

SELECT count(*), ll.law_name, ll.law_course, ll.law_lesson, 
       (CASE WHEN ll.score >= 0 THEN 'Done'
             WHEN ll.score < 0 THEN 'Not Done'
             ELSE 'Pending'
        END) as status
FROM users u JOIN
     law_courses ll
     ON u.id = ll.userid
GROUP BY ll.law_name, ll.law_course, ll.law_lesson, 
         (CASE WHEN ll.score >= 0 THEN 'Done'
               WHEN ll.score < 0 THEN 'Not Done'
               ELSE 'Pending'
          END);

SQL Query :: CASE条件

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