SQL根据具有多个值的一列添加标志

我试图在基于表的一列中添加一个包含多个值的标志。例如

Student_id |       Exam_type   
   123             Practice  
   123          Recertification
   123            Certification
   456             Practice
   456            Certification  
   789          Recertification
   135             Practice
   246             Practice
   246            Certification

我希望能够标记哪些学生参加了实践考试。 输出需要是：

Student_id | Practice_taken
123              Y
456              Y
789              N
135              Y
246              Y

---

您可以使用条件聚合和

大小写
表达式：

select student_id,
       (case when sum(exam_type = 'Practice' then 1 else 0 end) > 0
             then 'Y' else 'N'
        end) as practice_taken
from t
group by student_id;

您可以尝试使用row_number（）

其他选项是使用
exists
：

select student_id, (case when exists (select 1 
                                      from table t1 
                                      where t1.student_id = t.student_id and
                                            t1.Exam_type = 'Practice'
                                     ) 
                         then 'Y' else 'N' 
                    end) as practice_taken
from table t
group by student_id;

select student_id, (case when exists (select 1 
                                      from table t1 
                                      where t1.student_id = t.student_id and
                                            t1.Exam_type = 'Practice'
                                     ) 
                         then 'Y' else 'N' 
                    end) as practice_taken
from table t
group by student_id;