Question

我正在尝试理解以下查询，

SELECT s.LAST_NAME||', '||s.FIRST_NAME||' '||COALESCE(s.MIDDLE_NAME,' ') AS FULL_NAME,
s.LAST_NAME,
s.FIRST_NAME,
s.MIDDLE_NAME,
s.STUDENT_ID,
ssm.SCHOOL_ID,
ssm.SCHOOL_ID AS LIST_SCHOOL_ID,
ssm.GRADE_ID ,
sg1.BENCHMARK_ID,
sg1.GRADE_TITLE,
sg1.COMMENT AS COMMENT_TITLE,
ssm.STUDENT_ID,
sg1.MARKING_PERIOD_ID,
sg1.LONGER_COURSE_COMMENTS,
sp.SORT_ORDER,
sched.COURSE_PERIOD_ID 
FROM STUDENTS s,
STUDENT_ENROLLMENT ssm ,
SCHEDULE sched 
LEFT OUTER JOIN STUDENT_REPORT_CARD_BENCHMARKS sg1 ON (
sg1.STUDENT_ID=sched.STUDENT_ID 
AND sched.COURSE_PERIOD_ID=sg1.COURSE_PERIOD_ID 
AND sg1.MARKING_PERIOD_ID IN ('0','442','445','450') 
AND sg1.SYEAR=sched.SYEAR) 
LEFT OUTER JOIN COURSE_PERIODS rc_cp ON (
rc_cp.COURSE_PERIOD_ID=sg1.COURSE_PERIOD_ID 
AND rc_cp.DOES_GRADES='Y') 
LEFT OUTER JOIN SCHOOL_PERIODS sp ON (sp.PERIOD_ID=rc_cp.PERIOD_ID) 
WHERE ssm.STUDENT_ID=s.STUDENT_ID  
AND ssm.SCHOOL_ID='1'  
AND ssm.SYEAR='2010' 
AND ('22-APR-11' BETWEEN ssm.START_DATE AND ssm.END_DATE OR (ssm.END_DATE IS NULL))  
AND (LOWER(s.LAST_NAME) LIKE 'la''porsha%' OR LOWER(s.FIRST_NAME) LIKE 'la''porsha%' ) 
AND sched.STUDENT_ID=ssm.STUDENT_ID AND sched.MARKING_PERIOD_ID IN ('0','444','446','447','445','448','450','443','449') 
AND ('22-APR-11' BETWEEN sched.START_DATE AND sched.END_DATE OR (sched.END_DATE IS NULL AND '22-APR-11'>=sched.START_DATE))     
ORDER BY s.LAST_NAME,s.FIRST_NAME

并修改它以返回正确的结果 - 仅返回一个不同的人。搜索任何特定人员时，会返回多个结果，因为schedule.course_period_id返回了唯一值。由于course_period_id字段上有多个左外连接，但是在不同的表中，我对于在何处修改查询感到困惑。

Answer 1

我试图通过格式化您的查询并摆脱混合语法来帮助人们回答。不是一个答案，但评论太长了：

    SELECT s.LAST_NAME || ', ' || s.FIRST_NAME || ' ' || COALESCE(s.MIDDLE_NAME,' ') 
      AS FULL_NAME,
    s.LAST_NAME, s.FIRST_NAME, s.MIDDLE_NAME, s.STUDENT_ID, 
    ssm.SCHOOL_ID, ssm.SCHOOL_ID AS LIST_SCHOOL_ID, ssm.GRADE_ID ,
    sg1.BENCHMARK_ID, sg1.GRADE_TITLE, sg1.COMMENT AS COMMENT_TITLE,
    ssm.STUDENT_ID, sg1.MARKING_PERIOD_ID, sg1.LONGER_COURSE_COMMENTS,
    sp.SORT_ORDER, sched.COURSE_PERIOD_ID 
    FROM STUDENTS s
      INNER JOIN STUDENT_ENROLLMENT ssm
        ON ssm.STUDENT_ID=s.STUDENT_ID   -- moved from WHERE to here
      INNER JOIN SCHEDULE sched 
        ON sched.STUDENT_ID=ssm.STUDENT_ID -- moved from WHERE to here
      LEFT OUTER JOIN STUDENT_REPORT_CARD_BENCHMARKS sg1 
        ON (    sg1.STUDENT_ID=sched.STUDENT_ID 
            AND sched.COURSE_PERIOD_ID=sg1.COURSE_PERIOD_ID 
            AND sg1.MARKING_PERIOD_ID IN ('0','442','445','450') 
            AND sg1.SYEAR=sched.SYEAR) 
      LEFT OUTER JOIN COURSE_PERIODS rc_cp 
        ON (    rc_cp.COURSE_PERIOD_ID=sg1.COURSE_PERIOD_ID 
            AND rc_cp.DOES_GRADES='Y') 
      LEFT OUTER JOIN SCHOOL_PERIODS sp 
        ON (sp.PERIOD_ID=rc_cp.PERIOD_ID) 
    WHERE ssm.SCHOOL_ID='1'  
      AND ssm.SYEAR='2010' 
      AND ('22-APR-11' BETWEEN ssm.START_DATE AND ssm.END_DATE 
           OR (ssm.END_DATE IS NULL))  
      AND (  LOWER(s.LAST_NAME) LIKE 'la''porsha%' 
           OR LOWER(s.FIRST_NAME) LIKE 'la''porsha%' ) 
    AND sched.MARKING_PERIOD_ID 
         IN  ('0','444','446','447','445','448','450','443','449') 
    AND (   '22-APR-11' BETWEEN sched.START_DATE AND sched.END_DATE 
         OR (     sched.END_DATE IS NULL
             AND '22-APR-11' >= sched.START_DATE))     
ORDER BY s.LAST_NAME, s.FIRST_NAME

希望它有所帮助。

Answer 2

当然，如果加入的子表有多个同一个人的记录，那么你有多个记录。这是预期和正确的行为。

如果您只需要每人一条记录，那么您必须修改查询以告诉它您希望它选择多个子记录中的哪一条。但是，为什么你不想看到这个人的所有预定课程，而不是只有一个？

如果您必须使用group by，然后将聚合（如min或max）放在导致多个记录的字段上。但是，您仍然需要知道您是否只需要第一个期间记录或最后一个期间记录，或者您将如何决定您想要查看的人的六个记录？

Answer 3

Look up group by条款。

查询结果太多

3 个答案: