Question

这是我第一次进入＆＃34; stackoverflow＆＃34;。我刚刚开始我的编程最终项目并且遇到了sql查询的问题。（抱歉我的英语不好）

我有三个名为zstatistics，zsuggestions和ZEntrycriteria的表。我有一个sql查询，将＆＃34; UNION＆＃34; zstatistics，zsuggestions然后命令结果匹配最接近的结果。

    select M.* 
          from zstatistics M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code
          where C.Maths <= @maths
            AND C.Science <= @science
            AND C.English <= @english
            And C.Ict <= @ict
            And C.History <= @history
            And C.Geography <= @geography
            And C.Art <= @Art

UNION 

        select M.* 
         from zsuggestions M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code 
         where C.Maths <= @maths 
           AND C.Science <= @science 
           AND C.English <= @english 
           And C.Ict <= @ict And C.History <= @history 
           And C.Geography <= @geography 
           And C.Art <= @Art  
ORDER BY 

      sqrt( power(M.Maths - @maths, 2) + power(M.Science - @science,2) + power(M.English - @english,2) + power(M.Ict - @ict,2) + power(M.History-@history,2) + power(M.Geography - @geography,2) + power(M.Art - @Art,2))

我也试过了

select * from
(
select M.* 
          from zstatistics M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code
          where C.Maths <= @maths
            AND C.Science <= @science
            AND C.English <= @english
            And C.Ict <= @ict
            And C.History <= @history
            And C.Geography <= @geography
            And C.Art <= @Art

UNION 

        select M.* 
         from zsuggestions M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code 
         where C.Maths <= @maths 
           AND C.Science <= @science 
           AND C.English <= @english 
           And C.Ict <= @ict And C.History <= @history 
           And C.Geography <= @geography 
           And C.Art <= @Art  
)
ORDER BY 

      sqrt( power(M.Maths - @maths, 2) + power(M.Science - @science,2) + power(M.English - @english,2) + power(M.Ict - @ict,2) + power(M.History-@history,2) + power(M.Geography - @geography,2) + power(M.Art - @Art,2))

但我收到一个语法错误，说＆＃34;异常详细信息：System.Data.SqlClient.SqlException：如果语句包含UNION，INTERSECT或EXCEPT运算符，则ORDER BY项必须出现在选择列表中。＆＃34 ;

谢谢（编辑）

Answer 1

如果您想使用UNION，请将其放在查询之间。最后的查询就像

select * from
(
select M.* 
  from zstatistics M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code
  where C.Maths <= @maths
    AND C.Science <= @science
    AND C.English <= @english
    And C.Ict <= @ict
    And C.History <= @history
    And C.Geography <= @geography
    And C.Art <= @Art

UNION

select M.* 
from zsuggestions M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code 
where C.Maths <= @maths
  AND C.Science <= @science
  AND C.English <= @english
  And C.Ict <= @ict
  And C.History <= @history
  And C.Geography <= @geography
  And C.Art <= @Art
  ) t

 ORDER BY sqrt( power(t.Maths - @maths, 2) + power(t.Science - @science,2) + power(t.English - @english,2) + power(t.Ict - @ict,2) + power(t.History-@history,2) + power(t.Geography - @geography,2) + power(t.Art - @Art,2))

只要两个查询结果都有相同的列，那么您可以UNION这两个结果。

Answer 2

您可以在这两个查询之间使用union或union all，如mark所示。但是你需要知道UNION删除重复记录（结果中的所有列都相同），UNION ALL不会。

 select M.* 

  from zstatistics M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code
  where C.Maths <= @maths
   AND C.Science <= @science
    AND C.English <= @english
    And C.Ict <= @ict
    And C.History <= @history
    And C.Geography <= @geography
    And C.Art <= @Art

UNION

select M.* 
from zsuggestions M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code 
where C.Maths <= @maths
  AND C.Science <= @science
  AND C.English <= @english
  And C.Ict <= @ict
  And C.History <= @history
  And C.Geography <= @geography
  And C.Art <= @Art

如果您希望查询返回重复的行，您可以直接使用UNION ALL：

 select M.* 
  from zstatistics M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code
  where C.Maths <= @maths
   AND C.Science <= @science
    AND C.English <= @english
    And C.Ict <= @ict
    And C.History <= @history
    And C.Geography <= @geography
    And C.Art <= @Art

UNION ALL

select M.* 
from zsuggestions M JOIN ZEntrycriteria C ON M.coursecode=C.Course_code 
where C.Maths <= @maths
  AND C.Science <= @science
  AND C.English <= @english
  And C.Ict <= @ict
  And C.History <= @history
  And C.Geography <= @geography
  And C.Art <= @Art

如何使用加入查询的sql union

2 个答案: