select
    g1.Courseid,
    g1.GradeValue MinGradeValue,
    isnull(min(g2.GradeValue)-1,100) MaxGradeValue,
    g1.Description
from YourTable g1
    left join YourTable g2
        ON g2.CourseId = g1.CourseId
        and g2.GradeValue > g1.GradeValue
group by
    g1.Courseid,
    g1.GradeValue,
    g1.Description

SELECT courseId, description,
       gradeValue as minimumValue,
       LEAD(gradeValue) OVER(PARTITION BY courseId ORDER BY gradeValue) as nextGradeMinimumValue
FROM Grade

SELECT StudentGrade.studentId, StudentGrade.courseId, StudentGrade.grade,
       Grade.description
FROM (VALUES(1, 1, 38),
            (2, 1, 99),
            (3, 2, 74.5),
            (4, 2, 120)) StudentGrade(studentId, courseId, grade)
JOIN (SELECT courseId, description,
             gradeValue as minimumValue,
             LEAD(gradeValue) OVER(PARTITION BY courseId ORDER BY gradeValue) as nextGradeMinimumValue
      FROM Grade) Grade
ON Grade.courseId = StudentGrade.courseId
   AND Grade.minimumValue >= StudentGrade.grade
   AND (Grade.nextGradeMinimumValue IS NULL OR Grade.nextGradeMinimumValue > StudentGrade.grade)