如何在sql查询中输入条件

Question

I want to show all scored records in score table and student name in student table if column "flag" equal "shown". Else, if column "flag" in Score table equal "hidden" I will show all scored records with student name = "Student". Finally show all that in order of time.

Here is what I tried:

select s.student_name if h.flag = 'shown', select 'student' as s.student_name if h.flag = 'hidden',
   h.subject1_score,
   h.subject2_score,
   h.subject3_score,
   h.subject4_score,
   h.subject5_score,
   h.exam_date
from Score_Table h
join Student s on h.student_id = u.student_id
order by h.exam_date 

But that doesn't seem to work. What should I change? Thank you!

Answer 1

Your IF syntax is off. Read http://dev.mysql.com/doc/refman/5.7/en/control-flow-functions.html

select if(h.flag = 'shown',s.student_name,'student') student_name,
   h.subject1_score,
   h.subject2_score,
   h.subject3_score,
   h.subject4_score,
   h.subject5_score,
   h.exam_date
from Score_Table h
join Student s on h.student_id = s.student_id
order by h.exam_date 

Answer 2

The cASE i evolves as,

CASE WHEN h.flag = 'shown' 

It will check if the f.flag='shown' if true then it will select the s.studentName that is row value from table. And if the case is false then it will select the student as the StudentName .

You can also use the case as,

select 
     CASE WHEN h.flag = 'shown' THEN  s.student_name
     ELSE 'student' END AS StudentName,
   h.subject1_score,
   h.subject2_score,
   h.subject3_score,
   h.subject4_score,
   h.subject5_score,
   h.exam_date
from Score_Table h
join Student s on h.student_id = u.student_id
order by h.exam_date