Question

我有两张桌子

MARKS：

Roll
SubA（包含主题代码）
SubB（包含主题代码）
SubC（包含主题代码）
....
....

SUBJECT：

Sub_Code
Sub_Name
Sub_Opt（包含理论/实践等选项）

当我写这个查询时

Select 
    Roll, 
    (Select Sub_Name From Subject Wwhere dbo.marks.subA = dbo.subject.sub_code), 
    (Select Sub_Name From Subject where dbo.marks.SubB = dbo.subject.sub_code) 
from marks, subject

它成功运行，但是当我尝试在子查询中添加主题选项时 -

    select 
    Roll, 
    ( SELECT    Sub_name ,
                Sub_Opt
      FROM      subject
      WHERE     dbo.marks.SubA = dbo.subject.Sub_Code
    ) 
    ( SELECT    Sub_name ,
                Sub_Opt
      FROM      subject
      WHERE     dbo.marks.SubB = dbo.subject.Sbu_Code
    ) 
from Marks, subject

导致错误：

当EXISTS没有引入子查询时，只能在选择列表中指定一个表达式。

我想要这种格式的结果

ROLL, SUB_NAME_A, SUB_OPT_A, SUB_NAME_B, SUB_OPT_B, SUB_NAME_C, SUB_OP_C,......

Answer 1

如果join表中没有数据保证

，那么您可以LEFT JOIN在表格中SUBJECT代替内部

   SELECT  m.Roll ,
            a.Sub_name ,
            a.Sub_Opt ,
            b.Sub_name ,
            b.Sub_Opt
    FROM    marks m
            INNER JOIN SUBJECT a ON m.SubA = a.Sub_Code
            INNER JOIN SUBJECT b ON m.SubB = b.Sub_Code
            etc

Answer 2

选择滚，（SELECT Sub_name 来自主题 WHERE dbo.marks.SubA = dbo.subject.Sub_Code ）SUB_NAME_A，（SELECT Sub_Opt 来自主题 WHERE dbo.marks.SubA = dbo.subject.Sub_Code ）SUB_OPT_A，

( SELECT    Sub_name 
  FROM      subject
  WHERE     dbo.marks.SubB = dbo.subject.Sub_Code
)  SUB_NAME_B ,
( SELECT    Sub_Opt 
  FROM      subject
  WHERE     dbo.marks.SubB = dbo.subject.Sub_Code
) SUB_OPT_B ,

来自Marks

this also should work

如何在子查询中使用两个表达式

2 个答案: