我确信这是构建我的理解的一个简单问题，但我处于心理障碍中，并且可以使用一些洞察力。我的查询生成了太多行，我认为这是因为我没有正确使用我的子查询。如果有人有资源帮助我理顺它，我会很感激！
所需结果一行选择一个名称，实质上将单个课程名称转移到同一行（当某些数据匹配时）。
测试安装程序我必须在开发服务器上的现有表的上下文中工作，但子查询正确地创建了一个简单的注册数据表。对于开发目的，对于两个不同的学生，在给定子查询中填充的注册记录不超过两个。
输出块1始终正确显示（无论是注册数据还是NULL），块2将显示NULL或正确的数据，块3将显示NULL或正确的数据。
返回四行数据，一行包含所有正确数据（块1，块2和块3），三行数据不正确（块1，NULL，块3;块1，块2，NULL;块1 ，NULL，NULL）。
这是我到目前为止的完整代码（有很多垃圾）：
select distinct s.lastfirst as "Name",
s.home_room as "Teacher",
to_char(CASE WHEN (9000000 + satt.student_number) = s.student_number THEN satt.description END) as "School Absence",
to_char(CASE WHEN s.student_number = satt.student_number THEN satt.description END) as "Extended Day Absence",
to_char(CASE WHEN b1.studentid = s.id THEN b1.course_name END) as "Block 1",
to_char(CASE WHEN b2.studentid = s.id THEN b2.course_name END) as "Block 2",
to_char(CASE WHEN b3.studentid = s.id THEN b3.course_name END) as "Block 3",
' ' as "Signature"
from students s,
//Monday Block 1 Enrollment Generator
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to enter date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%2%') b1,
//Monday Block 2 Enrollment Generator
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to insert date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%4%') b2,
//Monday Block 3 Enrollment Generator
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to enter date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%6%') b3,
//Attendance record aggregator for the day specified
(select s1.student_number,
attc.DESCRIPTION
from ATTENDANCE att, students s1, ATTENDANCE_CODE attc, CALENDAR_DAY cd
where att.studentid = s1.id
and ATT_MODE_CODE = 'ATT_ModeMeeting'
and att.ATTENDANCE_CODEID = attc.ID
and att.calendar_dayid = cd.ID
//!!Need to insert date variable here
and to_timestamp('19-SEP-2016') = cd.DATE_VALUE) satt
where s.last_name='HappyPants'
//!!Need to insert teacher variable here
and s.HOME_ROOM = 'RadTeacher'
and s.schoolid = 6
答案 0 :(得分：0)
答案（男孩我觉得很傻）
我创建了一堆临时表，但（惊讶，惊讶）它是交叉加入。我在想，因为子查询中只有一条特定的记录可以匹配，所以它会在洗涤中出现。不。
添加LEFT JOIN与数据正确相关。
select distinct s.lastfirst as "Name",
s.home_room as "Teacher",
to_char(CASE WHEN (9000000 + satt.student_number) = s.student_number THEN satt.description END) as "School Absence",
to_char(CASE WHEN s.student_number = satt.student_number THEN satt.description END) as "Extended Day Absence",
to_char(CASE WHEN b1.studentid = s.id THEN b1.course_name END) as "Block 1",
to_char(CASE WHEN b2.studentid = s.id THEN b2.course_name END) as "Block 2",
to_char(CASE WHEN b3.studentid = s.id THEN b3.course_name END) as "Block 3",
' ' as "Signature"
from students s
//Monday Block 1 Enrollment Generator
LEFT JOIN
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to enter date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%2%') b1 on s.id = b1.studentid
//Monday Block 2 Enrollment Generator
LEFT JOIN
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to insert date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%4%') b2 on s.id = b2.studentid
//Monday Block 3 Enrollment Generator
LEFT JOIN
(select cc.studentid,
c.course_name,
cc.course_number,
cc.expression,
cc.DATEENROLLED,
cc.DATELEFT
from cc cc, courses c
where cc.EXPRESSION like '%A%'
and cc.SCHOOLID = 6
//!!Need to enter date variable here
and (to_timestamp('19-SEP-2016') > cc.DATEENROLLED and to_timestamp('19-SEP-2016') < cc.DATELEFT)
and c.course_number = cc.course_number
and cc.expression like '%6%') b3 on s.id = b3.studentid
//Attendance record aggregator for the day specified
LEFT JOIN
(select s1.student_number,
attc.DESCRIPTION
from ATTENDANCE att, students s1, ATTENDANCE_CODE attc, CALENDAR_DAY cd
where att.studentid = s1.id
and ATT_MODE_CODE = 'ATT_ModeMeeting'
and att.ATTENDANCE_CODEID = attc.ID
and att.calendar_dayid = cd.ID
//!!Need to insert date variable here
and to_timestamp('19-SEP-2016') = cd.DATE_VALUE) satt on s.student_number = satt.student_number
where s.last_name='HappyPants'
//!!Need to insert teacher variable here
//and s.HOME_ROOM = 'RadTeacher'
and s.schoolid = 6
order by lastfirst
答案 1 :(得分：0)
您的查询正在进行交叉连接，这就是您获得多行的原因。请尝试使用INNER JOIN