Question

使用MySQL。下面是我的表结构。

batch_admissions

------------------------+
batchId | studentId     |
----------------------- +
1       |   1           |
1       |   2           |
1       |   3           |
2       |   1           |
2       |   2           |
------------------------+

attendance_master

----------------------------+
attendance  | studentId     |
----------------------------+
P           |   1           |
P           |   2           |
P           |   3           |
----------------------------+

如果batchId=2如下所示，则需要结果，因为attendance_master只包含batchId=1的记录

----------------------------+
attendance  | studentId     |
----------------------------+
            |   1           |
            |   2           |
----------------------------+

但是目前我正在从attendance_master获取所有记录，而不管batchId的变化如何。我的查询有什么问题？我认为左联盟应该做的工作。但没有工作

SELECT 
            a.attendanceId, 
               a.attendanceDate, 
            a.attendance, 
            a.Remarks, 
            CONCAT(b.studentFirstName, ' ', COALESCE(b.studentMiddleName,'') , ' ', b.studentLastName) as studentName , 
            c.classRollNum,
            SUBSTRING_INDEX(SUBSTRING_INDEX( a.attendanceDate , '-', 3 ),'-',-1) AS attDay, 
            CASE WHEN DAYNAME(a.attendanceDate) = 'Monday' THEN 'Mon' 
                    WHEN DAYNAME(a.attendanceDate) = 'Tuesday' THEN 'Tue' 
                    WHEN DAYNAME(a.attendanceDate) = 'Wednesday' THEN 'Wed' 
                    WHEN DAYNAME(a.attendanceDate) = 'Thursday' THEN 'Thu' 
                    WHEN DAYNAME(a.attendanceDate) = 'Friday' THEN 'Fri'
                    WHEN DAYNAME(a.attendanceDate) = 'Saturday' THEN 'Sat'
                    WHEN DAYNAME(a.attendanceDate) = 'Sunday' THEN 'Sun'
            END as attDayName
,CONCAT(SUBSTRING_INDEX(SUBSTRING_INDEX( a.attendanceDate , '-', 3 ),'-',-1),'.',c.classRollNum) as Idx
FROM attendance_master a 
LEFT JOIN student_master b ON a.studentId = b.studentId 
LEFT JOIN batch_admissions c ON c.studentId = a.studentId AND c.batchId=1 
 WHERE a.attendanceDate BETWEEN '2016-03-01' AND '2016-03-31' 
ORDER BY c.classRollNum ASC


-------------

基本上我试图避免触发两个查询并希望在单个查询中得到结果。 batch_admissions表包含一系列批次，其中包含N个数学生。 attendance_master表保留了所有批次学生的出勤率。在网页上，我每批显示表格网格报告。我想要实现的目标，

case 1：当attendance_master不包含特定时段的batchId出勤时。仍然想要该批次的学生名单

-------------------------------------------------------
BatchId |studentId  |   Mon |   Tue |   Wed | Thus  |
------------------------------------------------------
1       |   11      |       |       |       |       |
1       |   12      |       |       |       |       |
..      |   ..      |       |       |       |       |

Case 2：当attendance_master包含特定时段的batchId出勤时。

-------------------------------------------------------
BatchId |studentId  |   Mon |   Tue |   Wed | Thus  |
------------------------------------------------------
2       |   1       |   P   |   P   |   P   |   P   |
2       |   2       |   P   |   A   |   P   |   P   |
..      |   ..      |   P   |   P   |   P   |   P   |

Alternate我可以触发两个查询来实现逻辑上的这个。一个用于批量学生，然后获得所有学生的出勤细节。

Answer 1

ok ...所以返回批量录取的所有记录和相关的student_master数据（总会有记录）和相关的考勤主数据......

FROM batch_admissions c 
INNER JOIN student_master b 
  ON a.studentId = c.studentId 
LEFT JOIN attendance_master a 
  ON c.studentId = a.studentId 
 and a.attendanceDate BETWEEN '2016-03-01' AND '2016-03-31'     
WHERE c.batchId=1 
ORDER BY c.classRollNum ASC

左连接不过滤结果

1 个答案: