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：

我尝试过使用GROUP BY student.StudentID但是它给了我不正确的结果。它在'2015-09-14'栏中显示'缺席'为'k1052280'而非现在。

我正在

我希望得到这个结果

  

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_1 FOREIGN KEY ( WorkshopID ) REFERENCES车间( 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{1}} {attendance_ibfk_1 {1}} {StudentID {1}} {学生{1}} {StudentID {1}}

     

), CONSTRAINT学生FOREIGN KEY (学生) REFERENCES学生(学生) ) ENGINE=InnoDB AUTO_INCREMENT=194 DEFAULT CHARSET=utf8;学生INSERT INTO学生VALUES ('k1052280', 'Ali Shaikh', 'k1052280@something.com', '101'); INSERT INTO学生VALUES ('k1052287', 'McKenzie Roth', 'Quisque@penatibus.edu', '102'); INSERT INTO学生VALUES ('k1052288', 'Dacey Sullivan', 'sollicitudin.adipiscing.ligula@semmollisdui.com', '103'); INSERT INTO {学生{1}}

     

VALUES ('k1052289', 'Callie Williamson', 'elementum@orciPhasellus.com', '104'); INSERT INTO出勤VALUES ('k1052290', 'Savannah Hyde', 'nec.metus.facilisis@nonummyut.co.uk', '101'); INSERT INTO出勤VALUES ('k1052291', 'Paul Tyson', 'semper.erat.in@ipsumleoelementum.net', '102'); INSERT INTO出勤VALUES ('k1052292', 'Nerea Ramos', 'gravida.sagittis.Duis@lacinia.edu', '103'); INSERT INTO出勤VALUES ('k1052293', 'Mark Mills', 'pellentesque.massa@blanditviverra.co.uk', '104'); INSERT INTO出勤VALUES ('k1052294', 'Zelda Cantu', 'ut@fringillaporttitorvulputate.org', '101');出勤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{ {1}}

Answer 1

这个查询可行 -

 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;

例 - 您可以在这样的列中使用子查询。

创建表：CREATE TABLE student（   id int（11）NOT NULL AUTO_INCREMENT，   name varchar（20）DEFAULT NULL，   主要关键（id） ）ENGINE = InnoDB AUTO_INCREMENT = 8 DEFAULT CHARSET = latin1;

创建表：CREATE TABLE attend（   id int（11）NOT NULL AUTO_INCREMENT，   stud_id int（11）DEFAULT NULL，   date varchar（20）DEFAULT NULL，   PRIMARY KEY（id），   KEY stud_id（stud_id），   约束attend_ibfk_1外键（stud_id）参考student（id） ）ENGINE = InnoDB AUTO_INCREMENT = 11 DEFAULT CHARSET = latin1

插入数据 -

INSERT INTO student（id，name）VALUES（1，＆＃39; hitesh＆＃39;），（2，＆＃39; mundra＆＃39;）， （3，＆＃39; sumit＆＃39;），（4，＆＃39; ashish＆＃39;）;  INSERT INTO attend（id，stud_id，date）价值观（1,1，＆＃39; 05-04-2015＆＃39;），（2,1） ，＆＃39; 05-04-2015＆＃39;），（3,1，＆＃39; 06-04-2015＆＃39;），（4,1，＆＃39; 06-04-2015＆＃39; ;），（5,2，＆＃39; 05-04-2015＆＃39;），（6,3，＆＃39; 05-04-2015＆＃39;），（7,3，＆＃39; 05-04-2015＆＃39;），（8,4，＆＃39; 06-04-2015＆＃39;）;

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;