根据另一个表中的数据从表中选择行

Question

Mentor table
------------
name (varchar)
contact (int)
english (boolean)
french (boolean)
german (boolean)


Student table
-------------
name (varchar)
contact (int)
english (boolean)
french (boolean)
german (boolean)

我想根据语言将导师与学生匹配，例如：

如果导师 1 懂英语和法语，他将匹配所有至少懂英语或法语的学生。

mentor1 (english, french)
-------------------------
studentA (english); 
studentB (english, french); 
studentC (english, german);
studentD (english, french, german)  

如果mentor2 只懂德语，他将匹配所有至少懂德语的学生。匹配的学生不仅会德语。

mentor2 (german)
----------------
studentC (english, german)
studentD (english, french, german)

通常我只会使用一堆if then else 来拼凑一个sql 字符串，但我使用gridview 来显示数据所以我不确定我能做什么。

欢迎提供示例代码和教程。

编辑：忘了提到mentor 表也将有name 和contact 等列。所以gridview 上的输出应该是每mentor 1 行。

Answer 1

Select
   m.MentorName
   , m.Language
   , s.StudentName
from Mentor as m
inner join Student as s
on (m.English = 1 and m.English = s.English)
    or (m.french = 1 and m.French = s.French)
    or (m.German = 1 and m.German = s.German);

如果您的表格结构中没有每种语言的字段而是一条记录，这会更容易

Table: Mentor(MentorName, Language)
Rows:
Mentor1 | English
Mentor2 | Englisn
Mentor2 | French

对学生做同样的事情，然后查询是：

Select
   m.MentorName
   , m.Language
   , s.StudentName

from Mentor as m
inner join Student as s
on m.Language = s.Language

这里的好处是，如果您添加另一种语言，它纯粹是数据输入，无需更改表结构或您的代码，但这并不总是一种选择。

Answer 2

SELECT  m.*, s.name
FROM    dbo.Mentor m
JOIN    dbo.Student s
ON EXISTS 
(
    SELECT  x.LanguageID
    FROM    
    (
        SELECT 1 AS LanguageID WHERE s.english = 1 UNION ALL 
        SELECT 2 AS LanguageID WHERE s.french = 1 UNION ALL 
        SELECT 3 AS LanguageID WHERE s.german = 1
    ) x
    INTERSECT
    SELECT  y.LanguageID
    FROM    
    (
        SELECT 1 AS LanguageID WHERE m.english = 1 UNION ALL 
        SELECT 2 AS LanguageID WHERE m.french = 1 UNION ALL 
        SELECT 3 AS LanguageID WHERE m.german = 1
    ) y
)
ORDER BY m.name