mysql - 对同一列进行多次计数并插入另一个表

Question

我有一个包含三列的学生表

1. Student Name
2. Class Name
3. Test result

一个学生参加了不止一项测试，结果不同。我正在尝试将数据放入另一个具有

1. Stundent Name+CLass Name ( Concatenated )
2. Pass (No of tests Passed)
3. Fail (No of tests failed)
4. Absent (No of tests Absent)

我用

select count(*)
from Student 
where Result in ('Passed')
group by StuName, ClassName;

获取每个 stu+class 组合的通过科目计数。对于失败和缺席的测试也是如此。

我应该如何修改代码以插入表二？

Answer 1

MySQL 支持内联 IF语句，

SELECT  CONCAT(StudentName, ' ', ClassName) Student_Class,
        SUM(test = 'PASSED') totalPass,
        SUM(test = 'Failed') totalFailed,
        SUM(test = 'Absent') totalAbsent
FROM    student
GROUP   BY CONCAT(StudentName, ' ', ClassName)

当你想插入上面查询的结果时，使用INSERT INTO..SELECT语句，

INSERT  INTO tableNAME(col1, totalPass, totalFailed, totalAbsent)
SELECT  CONCAT(StudentName, ' ', ClassName) Student_Class,
        SUM(test = 'PASSED') totalPass,
        SUM(test = 'Failed') totalFailed,
        SUM(test = 'Absent') totalAbsent
FROM    student
GROUP   BY CONCAT(StudentName, ' ', ClassName)

Answer 2

您可以使用具有以下功能的聚合函数轻松旋转CASE数据：

select concat(StuName, ',', ClassName) StuNameClass,
  sum(case when result = 'Passed' then 1 else 0 end) Passed,
  sum(case when result = 'Fail' then 1 else 0 end) Fail,
  sum(case when result = 'Absent' then 1 else 0 end) Absent
from Student 
group by concat(StuName, ',', ClassName);

然后，如果您想将数据插入到另一个表中：

insert into Table2 (StudentClassName, Passed, Fail, Absent)
select concat(StuName, ',', ClassName) StuNameClass,
  sum(case when result = 'Passed' then 1 else 0 end) Passed,
  sum(case when result = 'Fail' then 1 else 0 end) Fail,
  sum(case when result = 'Absent' then 1 else 0 end) Absent
from Student 
group by concat(StuName, ',', ClassName);

Answer 3

INSERT INTO t (name_class, passed_count, failed_count, absent_count)
SELECT CONCAT(StuName, ' ', ClassName) AS name_class, 
       SUM(IF(Result='Passed', 1, 0)) AS passed_count, 
       SUM(IF(Result='Failed', 1, 0)) AS failed_count, 
       SUM(IF(Result='Absent', 1, 0)) AS absent_count
FROM Student
GROUP BY StuName, ClassName;