Question

如果列“flag”等于“显示”，我想在学生表中显示得分表和学生姓名中的所有得分记录。否则，如果Score表中的“flag”列等于“hidden”，我将显示所有带有student name =“Student”的得分记录。最后按时间顺序显示所有内容。

以下是我的尝试：

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

但这似乎不起作用。我应该改变什么？谢谢！

Answer 1

您的IF语法已关闭。阅读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

cASE我演变为，

CASE WHEN h.flag = 'shown'

它将检查f.flag='shown'是否为真，然后它将从表中选择s.studentName作为行值。如果案例为假，则会选择student作为StudentName。

您也可以将案例用作

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

如何在sql查询中输入条件

2 个答案: