从 MySQL 中的多案例查询中删除重复项

Question

我有以下查询

 SELECT
    student.StudentID,
    student.`Name`,
    CASE
WHEN attendance.date = '2015-09-07' and attendance.StudentID IS NOT NULL THEN
    'Present'
ELSE
    'Absent'
END AS '2015-09-07',
 CASE
WHEN attendance.date = '2015-09-14' and attendance.StudentID IS NOT NULL THEN
    'Present'
ELSE
    'Absent'
END AS '2015-09-14'
FROM
    student
LEFT JOIN attendance ON student.StudentID = attendance.StudentID`

这给了我以下结果：

我曾尝试使用GROUP BY student.StudentID，但结果不正确。它在“k1052280”的“2015-09-14”列中显示“缺席”，而不是当前。

我来了

我想得到这个结果

CREATE TABLE学生( StudentID varchar(8) NOT NULL, 名称varchar(100) NOT NULL, 电子邮件varchar(254) CHARACTER SET latin1 NOT NULL, WorkshopID int(4) NOT NULL, PRIMARY KEY ( StudentID ), UNIQUE KEY StudentID ( StudentID ,电子邮件), KEY WorkshopID ( WorkshopID ), CONSTRAINT student_ibfk_1FOREIGN KEY (WorkshopID) REFERENCESworkshop(WorkshopID) ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE出勤( AttendanceID int(10) NOT NULL AUTO_INCREMENT, StudentID varchar(8) NOT NULL, 日期date NOT NULL, 时间time NOT NULL, PRIMARY KEY ( AttendanceID ), UNIQUE KEY unique_index ( StudentID ,日期), CONSTRAINT attendance_ibfk_1 FOREIGN KEY ( StudentID ) REFERENCES student(StudentID) ) ENGINE=InnoDB AUTO_INCREMENT=194 DEFAULT CHARSET=utf8;

INSERT INTOstudentVALUES ('k1052280', 'Ali Shaikh', 'k1052280@something.com', '101'); INSERT INTOstudentVALUES ('k1052287', 'McKenzie Roth', 'Quisque@penatibus.edu', '102'); INSERT INTOstudentVALUES ('k1052288', 'Dacey Sullivan', 'sollicitudin.adipiscing.ligula@semmollisdui.com', '103'); INSERT INTOstudentVALUES ('k1052289', 'Callie Williamson', 'elementum@orciPhasellus.com', '104'); INSERT INTOstudentVALUES ('k1052290', 'Savannah Hyde', 'nec.metus.facilisis@nonummyut.co.uk', '101'); INSERT INTOstudentVALUES ('k1052291', 'Paul Tyson', 'semper.erat.in@ipsumleoelementum.net', '102'); INSERT INTOstudentVALUES ('k1052292', 'Nerea Ramos', 'gravida.sagittis.Duis@lacinia.edu', '103'); INSERT INTOstudentVALUES ('k1052293', 'Mark Mills', 'pellentesque.massa@blanditviverra.co.uk', '104'); INSERT INTOstudentVALUES ('k1052293', 'Mark Mills', 'pellentesque.massa@blanditviverra.co.uk', '104'); INSERT INTOstudent@76

INSERT INTO出勤VALUES ('168', 'k1052280', '2015-09-07', '00:00:00'); INSERT INTO出勤VALUES ('169', 'k1052287', '2015-09-09', '00:00:00'); INSERT INTO出勤VALUES ('170', 'k1052288', '2015-09-11', '00:00:00'); INSERT INTO出勤VALUES ('171', 'k1052289', '2015-09-11', '00:00:00'); INSERT INTO出勤VALUES ('172', 'k1052290', '2015-09-14', '00:00:00'); INSERT INTO出勤VALUES ('173', 'k1052291', '2015-09-16', '00:00:00'); INSERT INTO出勤VALUES ('174', 'k1052292', '2015-09-18', '00:00:00'); INSERT INTO出勤VALUES ('175', 'k1052293', '2015-09-18', '00:00:00'); INSERT INTO出勤VALUES ('176', 'k1052294', '2015-09-21', '00:00:00'); INSERT INTO出勤VALUES ('177', 'k1052295', '2015-09-23', '00:00:00'); INSERT INTO出勤VALUES ('178', 'k1052296', '2015-09-25', '00:00:00'); INSERT INTO出勤VALUES ('179', 'k1052297', '2015-09-25', '00:00:00'); INSERT INTOattendanceVALUES ('183', 'k1052288', '2015-09-14', '00:00:00'); INSERT INTOattendanceVALUES ('187', 'k1052290', '2015-09-07', '00:00:00'); INSERT INTOattendanceVALUES ('188', 'k1052280', '2015-09-21', '10:30:00'); INSERT INTOattendanceVALUES ('193', 'k1052280', '2015-04-05', '00:00:00');

Answer 1

这个查询可以工作-

 SELECT Student.StudentID, Student.NAME, IF ( ( SELECT distinct 1 FROM attendance WHERE attendance.StudentID = student.StudentID AND date = '2015-09-07' ) = 1, 'Present', 'Absent' ) AS '2015-09-07', IF ( ( SELECT distinct 1 FROM attendance WHERE attendance.StudentID = student.StudentID AND date = '2015-09-14' ) = 1, 'Present', 'Absent' ) AS '2015-09-14' FROM student as student;

示例- 您可以像这样在列中使用子查询。

创建表：CREATE TABLE student ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(20) 默认为空， 主键 (id) ) ENGINE=InnoDB AUTO_INCREMENT=8 默认字符集=latin1;

创建表：CREATE TABLE attend ( id int(11) NOT NULL AUTO_INCREMENT, stud_id int(11) 默认为空， date varchar(20) 默认为空， 主键 (id), 键stud_id (stud_id), 约束 attend_ibfk_1 外键 (stud_id) 参考 student (id) ) ENGINE=InnoDB AUTO_INCREMENT=11 默认字符集=latin1

插入数据-

插入student (id, name) 值 (1, 'hitesh'), (2, 'mundra'), (3, 'sumit'), (4, 'ashish'); 插入attend (id, stud_id, date) 值 (1, 1, '05-04-2015'), (2, 1, '05-04-2015'), (3, 1, '06-04-2015'), (4, 1, '06-04-2015'), (5, 2, '05-04-2015'), (6, 3, '05-04-2015') '), (7, 3, '05-04-2015'), (8, 4, '06-04-2015');

结果查询

 select id , name , if((select distinct 1 from attend where stud_id=s.id and date = '05-04-2015')=1,'Present','Absent') as '05-04-2015' ,if((select distinct 1 from attend where stud_id=s.id and date = '06-04-2015')=1, 'Present' , 'Absent') as '06-04-2015' from student as s;