SQL：如何遍历SELECT语句的结果？

无需循环。您正在查看具有COUNT和GROUP的标准聚合。

当然，需要一些细节，但是原理是…

DECLARE @StudentId = 1DECLARE @Capacity = 20-- Classes will be the result of a Select statement which returns a list of intsIF EXISTS (SELECT *    FROM        Student.CourseSelections CS        JOIN        ---this is where you find out course allocations somehow        ClassTable C ON CS.classId = C.classId     WHERe        Student.CourseSelections = @StudentId    GROUP BY  --change this, it depends on where you find out course allocations        ClassID    HAVINg        COUNT(*) > @Capacity)   'no'ELSE   'yes'

编辑：

我已经更改了链接表。链接表中通常不需要Course_Student_ID。

现在加入

• 得到那个学生的课程
• 然后查看本课程中的所有学生并与能力进行比较

缩减以上版本：

...-- linking TableDECLARE @Courses_Students TABLE (,CourseId int,StudentId int)INSERT INTO @Courses_Students (StudentId, CourseId)VALUES (1, 1), (1, 3), (2, 1), (2, 2), (3, 2), (4, 1), (4, 2)DECLARE @StudentId int = 4--straight listSELECT     C.CourseName, C.Capacity, COUNT(*) FROM  @Courses_Students CSThis  JOIN  @Courses C ON CSThis.CourseId = C.CourseId  JOIN  @Courses_Students CSOthers ON CSOthers.CourseId = C.CourseId WHERe  CSThis.StudentId = @StudentId GROUP BY  C.CourseName, C.Capacity--oversubscribed list  SELECt     C.CourseName, C.Capacity, COUNT(*) FROM  @Courses_Students CSThis  JOIN  @Courses C ON CSThis.CourseId = C.CourseId  JOIN  @Courses_Students CSOthers ON CSOthers.CourseId = C.CourseId WHERe  CSThis.StudentId = @StudentId GROUP BY  C.CourseName, C.Capacity  HAVINg      COUNT(*) > C.Capacity