mysql - 将内部选择查询与主查询联接

Question

我想在我的课程管理系统中创建讲师的每月出勤报告。在此报告中，我需要使用嵌套选择查询来计算讲师在场和缺席的数量，以便在特定记录中显示它们。我认为可能的方法是，如果讲师代码与主查询中正在处理的讲师代码相同，则对要计算的每个出勤状态使用选择语句！

select lecturers.*, sum(distinct courses.credit) as 'Due Credits',(select count(*) from attendances where status='1' ) as Present, (select count(*) from attendances where status='0' ) as Absent from lecturers,courses,attendances
 where attendances.lecturer_code=lecturers.code 
 AND courses.lecturer_code=lecturers.code 
 group by lecturer_code

【代号、姓名、部门、​​职务、学历为固定属性】

我需要知道是否有更好的方法来做到这一点！

非常感谢！

Answer 1

SELECT   lecturers.*,
         SUM(DISTINCT courses.credit) AS `Due Credits`,
         SUM(attendances.status = 1)  AS `Present`,
         SUM(attendances.status = 0)  AS `Absent`,
FROM     lecturers
    JOIN courses     ON     courses.lecturer_code = lecturers.code
    JOIN attendances ON attendances.lecturer_code = lecturers.code
GROUP BY lecturer_code